First off, Urkel began as a breath of fresh air for my culture. "You mean black people are nerds, too? They're not all super aggressive athletes who commit violent acts at will! You're kidding me!"
Secondly, he and Fonz are, funny enough, very similar. They're both caricatures that are some what of an anomaly in their shows but ones that became the highlights of their shows because of it.
I think the modern equivalent is Amy Ferra Fowler. What started out as a side character has become the primary source of humor and interesting plot lines on the show. When she's not involved in an episode I don't enjoy it as much. The show has spent 5 seasons humanizing the least relateable human beings in existence and Amy comes along and just throws it all away...but in a good way. She's SO ridiculous and ostentatious in caricature that it trumps everything else.
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Realo won gold at the Sex Olympics with a BROKEN FRIGGIN NECK.-Voltch