Carl Urkel was played by Reginald VelJohnson, is the nerdy alter-ego of Carl in season 6's two-parter episode, To Be Or Not To Be, after he balked at Harriette's suggestion to see an opathomologist to get some glasses and asked Stefan to let him use his chamber to fix his dwindling eyesight (and perhaps make him more romantic in the process).
Character Background Edit
He was the unwitting victim of Myra's after she tampered with the Transformation Chamber thinking Stefan will use it to return as Steve and she can ensnare him. She soon realized her mistake and told Stefan to stop the chamber as she rewired the chamber and changed the setting from suave to nerd. Sure enough, the chamber is busted and Carl comes out as a nerd version of himself, complete with pocket protector and his boxers sticking out of his pants. It was soon revealed that he's half-Carl and half-nerd and Stefan has to fix the chamber to restore him back to normal. Carl spends the next few days walking a mile in Urkel's shoes, unwittingly being clumsy and enjoying things that Steve might like or does like, such as listening to the Bulgarian Women's choir, eating cheese and ironing his underwear. This caused the nerd genes in his body to accelerate rapidly.
One such visit at the Urkel basement, reveals that Stefan is having a hard time fixing the chamber because as cool and smooth as he is, he isn't as smart as he used to be. Carl's nerd side kicks in and reveals the mistakes of the parts he put in that were backwards. Soon Stefan gets annoyed with his antics and sends Carl home. A week after, he has finally fixed the Transformation Chamber and Carl is back to normal. After walking a mile as Steve, Carl realized he could've avoided this by taking Harriette's advice by getting glasses and sets up an appointment with an opathomologist.