TIS, great character! I wish I thought of him first. My favorite moment was when he was at a fancy party Elaine was hosting and the piano player didn't show up. So Jim offers to play. Elaine is freaking out but when he sits down he starts to play a beautiful classical song, then pauses and says "I must have taken lessons"

Two characters that pop into my mind right away are Norm and Cliff from Cheers. I loved all the characters on that show, but I was always waiting for one of Norm's funny comments, or Cliff's ridiculous trivia for everyone to laugh at.