Wow, once again my readers amazed me with the depth of their knowledge, and three correspondents got all the answers correct, which meant that I had to go with my predetermined tie-breakers.
#1. What color was the Joker's suit?
I had decided prior to the contest to accept purple as the color, since I believe I have mentioned that color a few times myself. However, this was the tie-breaker, as while researching the Joker's history I discovered that it was a very distinct shade of purple:
#2. Who was the son of the Joker?
Although he was never named specifically, in the story The Son of the Joker, he was described as the Joker's protégé.
#3. What crime boss willed his fortune to the Joker?
William "King" Barlowe willed his fortune to the Joker in The Joker's Millions (Detective #180). However, it turned out to be a trick, as Barlowe had placed a large amount of phony money and jewels with only a small amount of the real stuff as a gag on the Clown Prince of Crime.
#4. It is well-known that the Joker appeared in a story in the Golden Age which also featured the Catwoman, and another story where he teamed up with the Penguin. Who was the next super-villain to team-up with the Joker?
Lex Luthor teamed up with the Joker in the appropriately-named "Superman and Batman's Greatest Foes" in World's Finest #88.
5. Who was Gotham City's police commissioner in the 21st century?
Gotham City's police commissioner in the 21st century was Commissioner Rekoj, a descendant of the Joker who was as good as his ancestor was evil.
6. How did the Joker get his distinctive appearance?
In Detective #168, it was revealed that the Joker had gotten his bizarre look when he jumped into a vat of chemicals at the Monarch Playing Card Company to escape the Batman.
7. Was there a Bizarro Joker?
This was a tricky one and all my correspondents got it right for the wrong reason. There was a Bizarro Joker in the modern age, as revealed in DC Comics Presents #71. However, even before that the Joker was an honorary Bizarro. From World's Finest #156:
8. Who was the Joker's diminutive sidekick in the Silver Age?
Gagsworth A. Gagsworthy, better known as Gaggy, was the Joker's vertically challenged person of hench:
Aaron of Silver Age Gold, and "Jim" got all eight answers correct, as did Commander R. A. Benson, but only Commander Benson got the bonus point for coming up with "lavender" as the color of the Joker's suit, so he wins the tee shirt.
Thanks to Melanie of Nerdy Shirts for offering the prize; if you're looking for a cool, yet nerdy shirt, they're your source!