Assassin's Creed Odyssey takes place before all of the other Assassin's Creed games, including (oddly) the one called Origins. Still, it pays homage with a few winks and nods, and one particular cameo comes straight out of an Assassin's Creed game separated by a couple of millennia.
As noticed by JorRaptor on the Assassin's Creed subreddit, you can unlock Evie Frye as a lieutenant on your ship, the Adrestia. She provides a bonus to javelin and fire javelin damage as well as provide a damage boost while your health is low. She can be unlocked in the Ubisoft Club after completing the "Master Assassin" Challenge. That reward comes for reaching 7,500 XP in all Assassin's Creed games. That essentially rewards you for having played a prior game, since it will likely be unlocked from the start.
Evie is from Assassin's Creed Syndicate, the game set in 1800s London and the last one before Ubisoft took a year off to retool for Origins. Syndicate was also notably another game with dual male and female protagonists, though Evie and her brother Jacob were siblings who were both playable as part of the same story, rather than alternates like Alexios and Kassandra.
Other rewards that pay homage to the series history include Assassins and Medjay skins for your ship crew, alongside the usual boosts like XP, crafting items, and a variety of weapons. If you're getting ready to start up a game of Odyssey, be sure to check out our tips for beginners.
Assassin's Creed Odyssey is already available if you bought one of the special editions; otherwise it will be in stores Friday, October 5. Our review noted its "rich attention to detail for the era and its approach to handling the multi-faceted narrative with strong protagonists at the lead."