Legion may be filled with mutants, but it's light on the classic X-Men characters. That's fine except for the fact that David, who is famously Charles Xavier's son in the comics, is learning more and more about his past. What if Professor X isn't David's father on Legion? It is possible that the FX series is going in another direction.
Vulture theorized that David's father could be Oliver Bird. I'm a huge fan of Jemaine Clements in his role, so I wouldn't mind that revelation. They have similar powers, and David is already finding a family with Melanie at Summerland. How lovely was it that they all got to sit down to dinner together?
His father could also be The Eye, the Division 3 agent who captured David and Amy. Anybody is a potential candidate, really. It's weird because in most shows, if a main character doesn't know his birth parents and was plunged into such a mysterious world, we would assume that his dad is someone that we have already met. Star Wars, anyone?It's only because we know that the series is based on a Marvel comics character with an A-lister of a father does this mystery kind of fade away.
All in all, I'm pretty sure that the series is teasing Professor X as David's father. Even if he never shows up on the series, the clues are there. In Wednesday's episode, David drew him with no hair, alluded to him being British, and speculated that he had psychic powers. If that's a red herring, it's a pretty rude one.
That said, nobody has been cast in the role and it would be ultimately disappointing for David to be denied his father season, after season, after season. Supergirl ultimately showed us Superman, and Gotham is going to reveal the Joker eventually. These comic book elephants can't stay in the room unmentioned forever. Either Professor X is going to show up on Legion for real, or David's father is somebody else.