Marlon Brando
I think William Shatner is very similar to Marlon Brando.
They both have huge egos, both thought they were better than the rest.
Both seemed to be difficult to work with,many co stars from Star Trek have said how Shatner was difficult, he wanted his name bigger in the credits sequence, he tries to stand in front of others so he can have more of the screen.
Both gained a lot of weight in later years and can overact and be hammy at times.