Might I add, virtually single handily. This was inspired by these threads from another forum:
Characters who carried TV Shows (http://realwrestlecrap.proboards.com/index.cgi?board=offtopic&action=display&thread=377272&page=4)

Characters who single handily spoiled TV shows (http://realwrestlecrap.proboards.com/index.cgi?board=offtopic&action=display&thread=377218&page=1)

Well one person I think that completely made me fall in love with a TV show would be David Hyde Pierce in his portrayal of Niles Crane on Frasier. I never had any interest in all in Frasier but after I watched a few episodes, I found myself drawn to him. He is without a doubt my all time favorite character and I can say with complete honesty that if it weren't for him, I wouldn't be a Frasier fan at all. I do love the rest of the cast immensely, but there's just something about Niles that I find completely adorable!

Now the character that ruined a show would be CJ on "8 Simple Rules". I enjoyed watching the show when John Ritter was on, but once they added David Spade it just ruined it for me.