Rory Williams is played by Arthur Darvill and has one of the best progressive story arcs growing from slightly ineffectual to brilliant and brave.  He is insecure because, although he is Amy's fiance, he is afraid that she loves the Doctor more than him and he can never measure up. Of course, he shines through and proves himself a hero in his own right and Amy and Rory get married and (eventually) live happily ever after.  Rory is with the Doctor from 2010 to 2012