Elpenor made his living as a merchant, and this granted him many opportunities to serve the Sage of his chosen branch well. When the war between Athens and Sparta became apparent, Elpenor had already been supplying both sides with weapons.
When the Cult deemed it of utmost importance to find the members of King Leonidas I's bloodline, Elpenor sent out his informants to find both Myrrine and Kassandra. Two of these, Krethos and Antonide, were successful, finding Kassandra on the island of Kephallonia.
Dealing with Kassandra
Having located Kassandra's location, Elpenor travelled to the island, docking in Sami and took shelter in an abandoned house in 431 BCE. After witnessing Kassandra slaughtering his men first hand, Elpenor introduced himself to her, not before slaughtering the last man under his employment. Afterwards, Elpenor enlisted the help of the Spartan misthios Kassandra to retrieve Penelope's prized shroud, which had been stolen by bandits. He directed her to Odysseus' Palace on Ithaka to start her search. When Kassandra was successful in the task, Elpenor offered her to keep it as a reward. 
Elpenor soon proposed a new task to Kassandra: to hunt down and eliminate a Spartan general known as the Wolf who, unbeknowst to Kassandra, was her father, Nikolaos. The misthios later met Elpenor in his residence in Phokis and presented Nikolaos' helmet to him, whereupon he revealed he had known all along of Kassandra's relation to the Wolf. Upon confirming that Kassandra's mother Myrrine was alive, the cultist attempted to enlist the misthios to assassinate her as well but this only angered Kassandra, forcing him to summon his guards to delay the misthios while he fled.
Kassandra later learned of Elpenor's allegiance to the Cult of Kosmos from the Oracle of Delphi and resolved to track him down. Subsequently, Elpenor devised a trap by placing a decoy at Pharsalos Fort in the Valley of the Nymph but Kassandra killed the decoy, finding a letter revealing Elpenor's hiding place.
The letter from Elpenor detailed his orders to the decoy: kill the "so-called messenger of the gods" and meet him afterwards at the cave near the Snake Ruins within Valley of the Snake. When confronted once more by the misthios, Elpenor admitted that Myrrine was the Cult's only concern, and given that they already had Deimos, Kassandra might as well be dead. He fought Kassandra, but ultimately lost and was fatally wounded. With his dying breath, Elpenor declared that Kassandra had made a mistake in killing him, to which she retorted trusting him in the first place had been her mistake. He countered by telling her he was the only reason she'd ever left Kephallonia alive, given that the Cult wanted her death and his actions had spared her so far. As she tried to interrogate him about the Cult and their location, Elpenor merely chuckled before expiring.
Kassandra found on Elpenor a curious looking shard, as well as a symbol on his cloak: a single eye. Kassandra also found a set of robes and a white mask marked with red. All these things she took, believing they'd "come in handy".
In a simulation created by the Isu Aletheia, Elpenor's soul resided in the Underworld ruled by Hades. Elpenor worked for him numerous times, helping him to combat any prisoners of Tartaros who attempted to escape. On one occasion, Elpenor was deployed to eliminate a large group of prisoners in Hades' Palace. There, he came across Kassandra, who had managed to find her way to Tartaros and was helping Hades with his prisoners. Elpenor and Kassandra then interrogated an escaped prisoner of Tartaros on the location of the Monger, to which he revealed his location at the Lost Temple of Nyx. Kassandra required help obtaining the Armor of the Fallen, however, the Gauntlets of the Fallen were said to be lost. Elpenor was all too happy to assist her, instructing her to meet him at Kronos' Treasury.
After meeting him at the treasury, Kassandra and Elpenor searched the place for the fabled gauntlets. Thanks to Elpenor's knowledge of the Underworld, Kassandra was able to find them. Once Kassandra had retrieved the remaining pieces of the armor, Elpenor told her that it was time to send the Monger back to Tartaros. The two former enemies met at the Lost Temple of Nyx and launched their attack, defeating the Monger. Afterwards, however, Kassandra still had conflicting feelings about allying with Elpenor and she confronted him with Hades in attendance.
Legacy and Influence
Elpenor's death was later discovered by Deimos, who then decapitated Elpenor and brought his head to the Cult's meeting as proof of his death, which indirectly resulted in the grandchildren of Leonidas learning of each other's existence.
Some time later, Kassandra met a politician who claimed to be Elpenor's brother. Bemoaning Elpenor's murder, saying that Elpenor was a "kind and wealthy man" who had enabled him to join politics and even protected him, the statesman was afraid of losing what status he gained after bandits targeted him. Unaware of Kassandra's part in Elpenor's death, the man hired Kassandra to deal with the bandits.
Behind the scenes
- Assassin's Creed: Odyssey (first appearance)
- Assassin's Creed: Odyssey – Cultists: Elpenor
- Assassin's Creed: Odyssey – The Wolf's Fate
- Assassin's Creed: Odyssey – Fancy Guests
- Assassin's Creed: Odyssey – Penelope's Shroud
- Assassin's Creed: Odyssey – The Wolf of Sparta
- Assassin's Creed: Odyssey – The Truth Will Out
- Assassin's Creed: Odyssey – Snake in the Grass
- Assassin's Creed: Odyssey – Cult of Kosmos clues: Symbol on Elpenor's Cloak
- Assassin's Creed: Odyssey – The Fate of Atlantis: Torment of Hades – A New Lease on Death
- Assassin's Creed: Odyssey – The Fate of Atlantis: Torment of Hades – Arms of Atonement
- Assassin's Creed: Odyssey – The Fate of Atlantis: Torment of Hades – The Snake Sheds His Skin
- Assassin's Creed: Odyssey – The Serpent's Lair
- Assassin's Creed: Odyssey – Left for Dead