In Assassin's Creed Odyssey, the playable mercenary is called a misthios.
Misthios is a Greek term meaning a hired worker or mercenary, and the game uses it as a title for the protagonist, either Kassandra or Alexios. The player chooses which sibling to control, but the chosen character is consistently presented as a wandering mercenary during the Peloponnesian War.
This term is easy to confuse with other ancient Greek titles. A strategos was a military commander, an archon was a type of ruler or magistrate, and a dikastes was a judge. None of those is the protagonist's standard title in Odyssey.
The title fits the game's structure because the protagonist accepts contracts, travels between rival regions, and can work for different political factions. Odyssey is set in 431 BCE, during the early phase of the Peloponnesian War, and combines real historical figures and locations with the series' fictional First Civilization storyline.