AFAIK, Isildur1 was crushing a number of Euro sites (iPoker, Prima, Boss, etc) for quite a while, then moved his bankroll to Full Tilt. As atlanta said, he was also staked by TonyG off and on as well.
The two had a falling out after Isildur agree to play in the Party Poker
televised cash game staked by TonyG earlier this year and then backed out at the last second.
Don't believe stories of his turning $2k into $1m in 2 weeks or whatever. It's not the case. That said, he was certainly able to make $4m turn into 0 in just a few weeks at the hands of a number of FT Red Pros, primarily Brian Hastings and Brian Townsend if I recall correctly.