Joe Montana was one of many SF 49er quarterbacks to become a chief of the Chiefs. Joe Cool replaced Steve DeBerg as the `Niner starter. DeBerg then went to KC.
We all know who was next to go, Joe. Steve Bono was the next up in the SF to KC connection. Bono served as backup before Joe retired.
Later it was another rockstar named ex-49er, Elvis Grbac, to matriculate to the Chiefs.
Last in the lineage, Alex Smith completed the exodus, preceding Mahomes.
There's been one quarterback who has gone the other way. KC to SF. Can you name him without Google?