While 
Crusader Kings III allows players to select any landed ruler in either start date (867 or 1066), there are six bookmarks highlighting interesting characters to play. Many of these characters are required or otherwise well-suited for getting certain achievements.
867 start date
Wrath of The Northmen
"Two years ago, King Ælla of Northumbria threw the great Viking hero Ragnarr Loðbrók into a pit of snakes to die. Upon hearing the news, Ragnarr's sons set sail for England to avenge their father. The brothers have since established a firm foothold in York and The Isles. The Anglo-Saxon kings have lost battle after battle — their future looks bleak indeed. But all hope is not lost, and a great hero could still turn the tide of history. Will you lay all of England under Norse rule, or vanquish the Great Heathen Army from Anglo-Saxon soil?"
Halfdan Whiteshirt
"The first wave of the invasion has gone very well for Halfdan Whiteshirt. With the help of his brother Ivar, he has wrestled the control of York from King Ælla's hands. And he will take so much more. Will you follow in history's footsteps and have your bloody vengeance, or stake out a new path for Halfdan?"
Difficulty: Easy
Ivar the Boneless
""Rumors say that Ivar is weak of body, but no one can claim he is weak of mind. Through cunning and confidence, he has united a great number of Norse warbands under his banner, and won great victories on these foreign shores. But not even the greatest viking can cheat death. In 870, Ivar will fade from history forever... Can you win Ivar's wars, and keep him alive to rule for many years to come?#!"
Difficulty: Easy
Sigurdr Snake-in-the-eye
"As his brothers sailed off to England to exact their vengeance, Sigurd Snake-in-the-Eye stayed behind to rule his late father's lands. Ragnarr Loðbrók has left him some very large boots to fill.
Sigurd's descendants will be Kings of Denmark, Norway and England for well over a century. Can you fulfill the destiny of his dynasty?"
Difficulty: Medium
Björn Ironside
"Björn has lived a true Norseman's life of adventure. A fearsome raider, he has pillaged across France, Iberia, and Italy, together with his friend Hæsteinn of Nantes. Now, the forces of Scandinavia gather to assault British shores once more.
Though Björn is promised to avenge the death of his father in England, his descendants will rule Sweden for the next two centuries. On which side of the North Sea does your destiny lie?"
Difficulty: Easy
Earl Alfred the Great
"As the Vikings push further south, Earl Alfred of Dorset is readying his troops.
In the coming years, Alfred will fight numerous battles against the Norsemen and put an end to the invasion. When he inherits his brother's throne, he becomes one of the greatest English kings throughout history.
Will you fulfill Alfred's great destiny, or be crushed by the Great Heathen Army?"
Difficulty: Hard
The Great Adventurers
"Every dynasty comes from humble beginnings. The climb to power is usually a slow process, each generation moving a few steps up the ladder, through carefully planned marriages and ceaseless wars.
But these are times of great change and upheaval. With a lot of courage, and maybe a little luck, a hero might raise their family name from obscurity to legend. Are you ready to take on the challenge?"
Jarl Hæsteinn
"Through cunning and courage, Jarl Hæsteinn has become a rich man. After leading a lucrative raid through the Mediterranean together with Björn Ironside, Hæsteinn has settled in Brittany. The Franks have coffers ready for picking, and a mighty viking warrior makes a great ally in times of political turmoil.
Fortune does not come without enemies, however. Will Hæsteinn's greed get the better of him, or will his dynasty prosper under your guidance?"
Difficulty: Easy
Rurik Rurikid
"Few have risen from nothingness to greatness like the brave Rurik! Together with his brothers he brought order to the Eastern wilderness, and since their deaths, he is the lone ruler of a great Chiefdom. Yet, this is only the beginning.\n\n#bold One day, Rurik's descendants will found the Tsardom of Russia. Or will they? The destiny of this great dynasty rests in your hands."
Difficulty: Easy
Eudes Capet
"In July of 866, the viking raider Hæsteinn slew Eudes' father Robert the Strong. Mere months later, his mother Adelais died giving birth to his brother Robert. The world is cruel and the future might seem uncertain, but these orphan boys are destined to sit on the French throne. Their descendants, the Capets, will rule France for centuries to come.
Can you navigate the treacherous politics of medieval France and fulfill the destiny of the Robertine brothers?"
Difficulty: Hard
Álmos Árpád
"When the seven Hungarian tribes united to elect a supreme leader, their votes fell on brave Álmos. One day, his son Árpád will pick up the mantle — but only if the Hungarians can keep their independence. Danger looms on the Eastern horizon. Can you defend the Hungarians and lead them to greatness? This is your chance to retell the adventures of the Árpád dynasty!"
Difficulty: Medium
Daurama Daura
"As the Last Magajiya of Daura, Daurama is a symbol of the old ways of the Hausa people. Her new husband, Bayajiddah (originally from Iraq), represents change, as more and more outsiders flock to Hausaland, bringing their strange faiths and cultures with them... Daurama is set to go down in history as the Last Magajiva, but does she have to be?"
Difficulty: Medium
The Carolingians
"After the passing of Louis the Pious, the once-great Carolingian Empire was divided up into the three separate Kingdoms of East, West, and Middle Francia. Since then, these realms have only splintered further as wars, rebellions, and inheritance variously cause instability and fragmentation.
Are any of the Karlings strong enough to reunite their empire? Or will their family squabbles leave them vulnerable to exploitation by opportunists?"
Charles the Bald
"At the time of Charles' birth, his fully grown half-brothers already ruled their own kingdoms within the Carolingian empire. Without a crown of his own, he became known as 'the Bald,' though he eventually did inherit Aquitaine and West Francia. In the future he will even inherit Italy and the Holy Roman Empire itself, but his line will not persevere — his last grandson will die childless just seven years after his own death. Can you change the course of history and ensure a long and prosperous line of Charles' decedents?#!"
Difficulty: Medium
King Lothaire II
"Though he was in love with his mistress Waldrada, Lothaire's father forced him into a political marriage with Teutberga. Their union produced no children, and Lothaire's life has been a continuous struggle to divorce his wife and get his bastard children legitimized. Though he never stops trying, Lothaire will go on to die without a legal heir. Can you overcome the machinations of those who plot against you and ensure the continuation of your house?#!"
Difficulty: Medium
Ludwig the German
""An ambitious man, Ludwig has long sought to reconquer the pieces of the Empire he considers his birthright. These ambitions have suffered from setback after setback however, as his various military campaigns all ended in failure and his rebellious sons have pried away most of his own lands from his control. Can you reverse Ludwig's misfortunes and regain the Empire for his descendants, or are his sons destined to be relegated to a mere footnote in history?"
Difficulty: Medium
King Louis II
"Imperial power had diminished so much by the time Louis was crowned Holy Roman Emperor that the title no longer offered any real authority. Though he managed to reclaim the Kingdom of Provence, Louis' uncles and brother, unburdened by any sort of allegiance to the Imperial Crown, continue to act as they please. Saddled with quarrelsome neighbors and an unstable realm, Louis II will die before siring a son.
Can you regain all the lost territories of the Empire and reestablish the Imperial Crown as a real power?"
Difficulty: Medium
Prince Karlmann
"The eldest son of Ludwig the German, Karlmann rebelled against his father and forced him to give him control over the lands of Bavaria. He will expand this domain in wars with Slavs to the east and later on will even be elected King of Italy — though an unfortunate stroke will force him to abdicate the thrones of Bavaria and Italy to his younger brothers. He will die just a few years later.
With a little luck, will you be able to avoid Karlmann's unfortunate demise and establish a legacy that will last the ages?"
Difficulty: Medium
1066 start date
The Fate of England
"When the childless King Edward the Confessor died it plunged England into a succession crisis unlike any that had come before. Three men attempted to secure the throne for themselves: Harold Godwinson, William the Bastard, and Harald Hardrade, while Svend and Malcom stood by, ready to pounce at any sign of weakness. Who will stand victorious after this tumultuous time in history?"
King Harold of England
"Harold Godwinson was the leader of a powerful noble house, and the brother-in-law of the King, when the childless King Edward died. Now, elected the new King of England by his peers, he is faced with the challenge of holding onto the throne, as the covetous Duke of Normandy, as well as King Harald of Norway, spurred on and aided by Harold's exiled brother, seek to replace him! With a large army at your back and the support of the Anglo-Saxon lords — will the wolves find that they have bitten off more than they can chew?"
Difficulty: Hard
William the Bastard
""The House of Normandy trace their lineage back to Norse vikings, and established themselves on the mainland of Europe over 200 years ago. Now, William II dreams of leading his family to rule the Kingdom of England, and he believes his status as successor to the throne was promised by the late King Edward, and even recognized by Harold Godwinson himself. However, now that Edward is gone, Harold has broken his oath and taken the crown for himself! William is at war with England. Can you muster your forces and claim what is rightfully yours?"
Difficulty: Medium
Harald Hardrada
"Having displayed formidable military talent since youth, Harald has recently tried, and failed, to conquer Denmark. Now, he looks beyond the sea — by ancient contract, the crown of England should have passed to Harald, when the last King died without an heir. But, instead, the Anglo-Saxons have put Harold Godwinson on the throne! Luckily, the false King has made enemies, and Tostig Godwinson, Harold's own brother, lives in exile in Norway... By using his own enemies against him, can you give this Varangian viking control over the North Sea?"
Difficulty: Medium
King Svend of Denmark
"With blood ties to England and Norway, Svend has strong claims to both thrones. Unfortunately, his armies are small and undisciplined, making a war of conquest unfeasible. However, there are other ways to pursue one's dreams... If your children were to be married into powerful families, it could grant many useful alliances — alliances you could leverage to found an empire that would rival Rome itself!"
Difficulty: Easy
King Malcolm of Scotland
"Known to Scotland as the "Great Chief", Malcolm III's situation is tenuous, but full of opportunity. To the south, the rich lands of Northumbria lie vulnerable as England is torn apart by war, but Norse warlords and Gaelic highlanders yet contest the king's rule at home. The British Isles teem with dangers and opportunities: can you pluck a rose from this garden of thorns?"
Difficulty: Easy
Rags to Riches
"Throughout Europe, families fight and scheme for power. A lot of land lies disputed, as battles are won and lost, and dynasties come and go, as their rulers are outmaneuvered.
Kings of old are being replaced, while newcomers reach for the stars. Which will you be?"
Most of these characters are well-suited for beginners.
Petty King Murchad
"In the beginning of the 11th century, the High Kingship of Ireland has fallen in and out of house Briain's grasp, as the Irish noble houses have warred over territory, against each other and Viking settlers. Yet, while hailing from a line of men deemed destined for Kingship, not much is known about Murchad's brief reign over the smaller area of Munster. With your help, perhaps a member of the house of Briain can sit on the throne of Ireland once more?"
Difficulty: Easy
As in Crusader Kings II, Murchad is recommended for players new to Crusader Kings III, and is used for the in-game tutorial mode. As the strongest ruler of Ireland in 1066 start date, he can easily form the Kingdom of Ireland, getting the Emerald Isle achievement.
Duchess Matilda
""By skill or circumstance, Matilda of Canossa is destined to inherit a substantial territory in Northern Italy. She will move on to become a powerful and well-connected ruler, eventually rising to the unique rank of Imperial Vicar and Vice-Queen of Italy. Long after her death, she shall remain a figure legendary for both her piousness and suspected witchcraft. Can you ensure Mathilda's legacy endures, and continue the Canossa line for generations to come?"
Difficulty: Medium
Emir Yahya
""The Kingdom of Toledo will be established in the late 11th century, when the King of León takes over the eponymous city. This eradication of Emir Yahya and his influence means that the Dhunnunid family will lose its hold on the region, where they have reigned for generations. Through manipulating your rivals, and finding more allies, do you have what it takes to challenge the Kings of the Iberian peninsula and change history for the Dhunnunid house?"
Difficulty: Medium
Duke Vratislav
""The Přemyslid family has ruled the region of Bohemia for hundreds of years. They have relied heavily on Seniority for their succession, which, in Duke Vratislav's case, will eventually lead to serious strife with his brothers. To become King of Bohemia, Vratislav will need to be tactical with his resources, both material and not — are you up for the task?"
Difficulty: Easy
Duke Robert 'The Fox' de Hauteville
"Robert started out his career a thief and head of a band of highwaymen. Being one of many siblings, the adventurous son was never predicted to become a brilliant strategist and statesman, ruling vast areas of land — yet here he is, a powerful Duke of southern Italy, ready to take on the path of history, which will enable the Hautevilles to have a foothold in Sicily for over a hundred years. If you can consolidate the power in the realm, the Kingdom of Sicily awaits its ruler!"
Difficulty: Medium
Iberia in Pieces
'"When the old king Ferdinand I passed away his three sons all inherited a piece of his Iberian kingdom. Greed, ambition, and holy wars soon push the Iberian Peninsula to boil, and the bonds between family members start to fray. Are any of the Fernandez siblings strong, or cunning, enough to emerge victorious over the rest? How will war and diplomacy mold the Iberian peninsula?"
King García
"Given the most troubled kingdom of the three brothers, García tried many extreme remedies to stabilize his rule. However, the fragile land was soon too tempting for his brother Alfonso who invaded in 1071. This attack kicked off the many wars that followed between the brothers, but García would spend most of this time behind bars. Take up arms against your brothers and lead this unstable kingdom to glory and victory!#!"
Difficulty: Medium
King Alfonso VI
"The middle son, and his father's favorite, Alfonso inherited the rich middle kingdom of León. He moved on to outsmart and subjugate both his brothers, and he ruled over the reunited kingdom of his father.
Through political and familiar diplomacy and aggression, do you have what it takes to unite the three kingdoms under one banner?"
Difficulty: Easy
King Sancho II
"Sancho was cheated out of his full inheritance by his father's division of the land among all three brothers. A man of opportunity, he quickly took up arms against his brothers as soon as the peace started to crumble, but only briefly got to rule the reunited kingdom before he was assassinated. Through military action and planning, can you restore the full kingdom to its glory under the one rightful ruler, and hold on to power?"
Difficulty: Medium
Infanta Urraca
"The oldest of Ferdinand's children, Urraca had widespread influence over both her brothers and the Church. She and her sister Elvira received lordship over all the monasteries in the three kingdoms, and she did not sit idly by as her brothers tore each other apart. To outmaneuver her brothers and secure her place in history Urraca needs both patience and daring – will you succeed?"
Difficulty: Hard
King Antso IV
""Many lords in the west of the kingdom deserted King Antso after he ascended to the throne following the passing of his parents. He was soon embroiled in a war with his cousin King Sancho which saw Antso defeated, and after a rule marked by warfare and defeat he was assassinated by his own siblings.
Rewrite history, outsmart your family, and secure your domain and heritage!"
Difficulty: Hard