I've been reading too much of TV Tropes lately and was laughing my ass off in remembrance of the genre of gaming tropes known as "That One Boss"...

Basically its the Boss of the game that is not the Final Boss or some super powerful optional boss, it's just a regular boss who seems to be in a league of his own compared to everything else in the game and is insanely hard for one reason or another. The other clincher is that it is not a boss that has some trick to them unless its a trick you had no chance in hell of knowing about.

So who do you think is the most notorious "That One Boss" in gaming?