|This article is about the King of Sparta. You may be looking for The False Leonidas.|
A direct descendant of the Isu, Leonidas possessed a proportionally-higher level of Isu genes than usual; consequently, so did his descendants. He also wielded an Isu spear, which was later passed down to his daughter Myrrine, and then his granddaughter, the misthios Kassandra. Through his granddaughter, Leonidas is also an ancestor of Aya of Alexandria, who, along with her husband, the Medjay Bayek of Siwa, would go on to found the Hidden Ones, the forerunners of the Assassins.
For his defiance against the Cult of Kosmos, Leonidas' descendants came to be targeted by the Cult, who sought to have his bloodline wiped out such that they would no longer face opposition against their plans.
Opposition against the Cult
- Cultist: "Enough! We have grown tired of your insolent tongue! Sparta will not go to war, the Pythia has spoken!"
- Leonidas: "The Pythia says what you tell her to say! She's been your puppet for far too long, the time has come to cut her strings!"
- —Leonidas opposing the Cult's wishes, 480 BCE.[src]-[m]
In 480 BCE, Greece was invaded by the Achaemenid Empire under the reign of Xerxes I, who was secretly backed by both the Order of the Ancients and the Cult of Kosmos. Leonidas consulted the Pythia in Delphi about going to war against the Persians. The Cult of Kosmos, who had manipulated the Pythia for generations, were present during his consultation and threatened Leonidas not to go against their plans. However, Leonidas defied the order and commanded his officer, Dienekes, to gather the army for battle.
Battle of Thermopylae and death
Leonidas and his army gathered at a narrow passage way in Malis, where the Persians would have to pass through in order to reach mainland Greece. Prior the battle, Leonidas reminisced to Dienekes about how he would have liked to have gone fishing with his son. Upon spotting the arrival of the Persian fleet in Malis, Leonidas briefed his men and braced for the attack. During the first wave, Leonidas clashed and defeated a Persian officer, Kurush. 
In the aftermath, one of the Spartans revealed that they had been betrayed by one of the Greek soldiers, Ephialtes of Trachis, who revealed a path behind the passage which allowed the Persians to maneuver around. Nevertheless, Leonidas refused to retreat and ordered his men to defend the pass. The Spartans were able to defend the passage for seven days, though they were eventually overwhelmed. Soon after the death of Dienekes, Leonidas himself perished, but not before killing a Persian officer who delivered a mortal injury to him.
Following Leonidas' death, Xerxes, who was otherwise recognized for his civility and honor when dealing with his fallen foes, had been so deeply infuriated by Leonidas' defiance that he had his head cut off and impaled on a pike. His remains, along with his spear, were later recovered and returned to Sparta, where he was buried in a tomb southwest of the city, while his broken spear was handed down to his daughter, Myrrine, who in turn passed it on to her daughter Kassandra.
When the Isu Aletheia created a simulation of Elysium for the Leonidas' descendant Kassandra to better learn how to wield the Staff of Hermes Trismegistus which Pythagoras had passed on to her, she met a simulant Leonidas within.
Personality and characteristics
Leonidas was shown to deeply care for Sparta and those who inhabit it, as he was willing to defy the Cult and defend his home to the death. Following the Battle of Thermopylae, Leonidas was noted for his great courage, as he bravely fought to the death against the Persians despite their overwhelming numbers.
Leonidas was also mentioned as having a hard to control temper. A good example of his temper would be from the Battle of Thermopylae: when presented with a Persian soldier gloating about Leonidas' imminent defeat, Leonidas immediately thrust his spear head through the man's mouth to silence him. This temper, and Leonidas' trouble keeping it in check, was also well-remembered after Leonidas' death, as Archidamos noted when meeting Kassandra around 429 BCE.
He also had a sentimental side, as during the Battle of Thermopylae, he told Dienekes how he would've liked to have gone fishing with his son Pleistarchus, and while fishing with Kassandra in Elysium, he reflected how his mother told him that his spear carried a certain burden, but he was ready; he is also very cunning, as while fishing with Kassandra in Elysium, he was able to immediately deduce that Persephone had sent her to kill him.
Behind the scenes
- Assassin's Creed: Odyssey (first appearance)
- The Fate of Atlantis: Fields of Elysium (simulation only)
- Assassin's Creed: Rebellion
- Assassin's Creed: Valhalla – Assassin's Creed Crossover Stories (mentioned only)
- Assassin's Creed: Brotherhood of Venice (mentioned only)
- Totilo, Stephen (11 June 2018). Everything We Learned About Assassin’s Creed Odyssey [sic] After Playing It. Kotaku. Archived from the original on June 12, 2018. Retrieved on June 13, 2018.
- Assassin's Creed: Odyssey – Legacy of the First Blade: Hunted – Protector of Persia
- Assassin's Creed: Odyssey – Bully the Bullies
- Assassin's Creed: Odyssey – Battle of 300 (memory)
- Assassin's Creed: Odyssey – Memories Awoken
- Assassin's Creed: Odyssey
- Assassin's Creed: Odyssey – The Fate of Atlantis: Fields of Elysium
- Assassin's Creed: Odyssey – Kings of Sparta