I don't know if I'm capable of playing a serious character, so there's a rich tapestry to pull from here:

For a Christmas one-shot I played a Santa Claus impersonator with a warhammer. He was my Maul Santa.

The most whimsical was a gnome alchemist (I think he was a wizard, but we like styling up our spells). He owned a soda pop empire and was adventuring for rare ingredients. Basically he was a Willy Wonka type and I called him Dr Pibb

Silliest was probably my short, swarthy, greased-up masked wrestler. Glorious indeed were the bouts of El Cabron the Luchadwarf