Amongst the various other atrocities committed when Xavier went all nutso and became all-powerful villain Onslaught (more on that later, true believers!) was the long-building revelation that the fatherly Professor had some less-than-fatherly feelings towards one of his earliest recruits; namely, the fatally unlucky fellow psychic Jean Grey. I will say up front, that Xavier recruited and taught Jean from when she was a child, unlike the other original X-Men. Ew. There's actually been a bunch of references to Xavier having romantic designs on Marvel Girl - including an off-handed remark in an early issue, more recently in the Ultimate universe, and (creepiest of all) during Jean's marriage to Cyclops when she says how she thinks of him as a father - but it was during the Onslaught debacle that Jean, trying to get at the sane Xavier beneath all the 90s angst, was faced with the fact that her father figure totally wanted to bang her. The sleazy jerk.
Tom Baker is the Comics Editor at WhatCulture! He's heard all the Doctor Who jokes, but not many about Randall and Hopkirk. He also blogs at http://communibearsilostate.wordpress.com/