One of the most fun little extras in Assassin's Creed games has to be the ability to utilize different suits from past heroes.
It's a fun little reward and a way to naturally link things together: almost like you found their old armor and are continuing their legacy (one game makes this explicitly clear). But in Odyssey, you can also just recruit old characters in an Easter Egg sort of way, like Evie from Syndicate or now: Bayek from Origins.
To grab him you basically just need to dish out 50 points on the Club Ubisoft app, which you can access online or in-game. That's roughly one Club achievement's worth of points if you're naturally playing Odyssey.
Assassin's Creed [Twitter]