Which are your greatest sports "traitors"?

So basically athletes who used to compete for one team and then switched to a rival team to the irritation of the original team's fans. I know a few as examples:

-Ionel Dănciulescu - played for Dinamo Bucharest, then moved to mortal rivals Steaua Bucharest and then moved back to Dinamo.

-Nicolae Stanciu - played for Sparta Prague and then moved to rivals Slavia, i know one guy who calls him "the rat" because of it ahah.

-Luis "El Traidor" Figo - probably the most famous such footballer in Europe, moved from Barcelona to Real Madrid which caused a huge outrage on part of the Barcelona fans. Aside for money it's still not clear for me why he did it, maybe someone has extra context.