His 74-game winning streak ended on November 30, 2004.
On November 30, 2004, Ken Jennings, the software engineer from Salt Lake City, Utah, ended his 74-game winning streak on Jeopardy! After winning more than $2.5 million* over his run, Jennings was defeated by Nancy Zerg during Final Jeopardy.
*Yes, I know Jennings has made subsequent special appearances on Jeopardy! and won even more money than that, but we're just going to deal with this specific episode.
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via BuzzFeed/Travel