Sherman’s pensive sidekick provides the anchor of sensibility for an otherwise eccentric cast. Not that Fillmore is a normal, well adjusted sea turtle; far from it. He’s bookish and slightly pompous and arrogant, however he’s sensitive and principled, and right most of the time (http://shermanslagoon.com/meet-the-cast/). He has the misfortune to strike out every time he goes looking for a mate. Sometimes he strikes out due to his hopeless nerdiness, his complete lack of an ability to even engage in a full conversation with a girl, or his hideously smelly and overpowering cologne, or his pompous, arrogant attitude.
Another interesting fact about Fillmore is that he seems to be completely unaware of his own faults, or if he is aware of them he refuses to acknowledge them.