I believe the Joker comes from "Jucker" the ?? name for Euchre since the card was originally intoduced for the games of the Euchre family.
Just for fun, did you know that the face cards have names?
Kings of Spades-David, Hearts-Charlemagne ( or suicide king, because of the sword in the head thing!), Diamonds-Julius, Clubs-Alexander---Queens of Spades-Joan, Hearts-Judith, Diamonds-Rachel, Clubs-Argine (anagram of Regina which is Latin for Queen. The Jacks I am not sure of I know the Jack of Clubs is Lancelot and the Jack of Diamonds is Hector