T-Rex, Tomb Raider
OK, it's not really a boss and less forgiving gamers out there may feel the scariest thing about Tomb Raider's T-Rex is that those PSone polygons could cut your eyeballs. But if you played it at the time, you'll never forget that first encounter.
Above: Now this calls for a more urgent tactic than Lara's trademark 'run gently in circles shooting'
Although the raptors on the loose in the Lost Valley level should have clued you in that evolutionary rules weren't going to apply, the screen-thundering lizard's appearance - which, thanks to a brutally short draw distance, really did come out of nowhere - is responsible for knocking hours off the lifespans of many in the PlayStation Generation.