Pride is known as the Deadly Sin that all other Sins stem from. I was thinking about that last night, and it occured to me that since that's true, should Pride be "Father"? It's not mentioned how old he is or anything.
There are lots of problems with this though. Who created "Father"? Randomness involving his health and wires and stuff (unless I'm misinterpreting the huge ass tube-thrown thingy as a life-support thing, and it's really just a funky design).
But I personally find "Ed is the manga Pride" a crackpot theory. ... Then again, I also thought that Ed's father making Envy in the anime was a crackpot theory myself, and look where that got me.