Marat was stabbed in the bath by Charlotte Corday; he had a skin condition alleviated by resting in warm water. That's fairly obscure knowledge; most people (including me) only know it because there is a famous painting of the scene, more famous now than Marat is.
I think that answer will down in TV quiz history, Richard and Alexander couldn't stop laughing, now Gemma (the contestant) will be famous as know doubt the clip will shown and talked about constantly, beats name a bird with a long neck Naomi Campbell (Family Fortunes)
I only knew Marat because I had just finished a quiz about famous women. One question was who stabbed a famous revolutionary in his bath. Had to look it up and got both names.