"Amok Tim"
The Enterprise crew come across a planet with one lone being on it named Tim.
Tim's Arrow
A rift in time opens up and sucks some guy named Tim into the future. Tim is kind of an ass, but apparently this had some kind of butterfly effect impact on the past which prevented WW3, preventing man from ever overcoming it's differences and founding the Federation. So they have to send Tim back to the past and help him accidentally cause WW3.
Tim keeps making obnoxious comments. Data ends up smacking him upside the head, bringing him one step closer to understanding what it means to be human.
Further adventures of the time-travelling Tim (no relation!):
"The Naked Tim" - Tim gets drunk and stumbles around the Enterprise, au naturel.
"The Tim Trap" - To stop that jerk Tim, Captains Kirk and Kor team up (at the behest of the galactic community) and plan a way to trap Tim and his obnoxious behavior.
"Tim Squared" - Tim messes around with the time rift again, and creates multiple versions of himself, annoying the Enterprise crew and Captain Picard. Picard gets fed up and finally straight-up murders the original Tim. Or did he?
"A Matter of Tim" - Tim comes back from a vacay to the 22nd century with all sorts of Enterprise-related memorabilia. Worf, not wanting to acknowledge Enterprise as canon, places Tim under arrest.
"Tim Escape" - Tim escapes from prison, and enlists the Romulans to aide him in pranking the Enterprise. They go a bit overboard.
"Hard Tim" - Miles O'Brien runs across a sex tape created by Tim. He's scarred for life.
"Children of Tim" - Tim sabotages the Defiant to form an alternate timeline where he doesn't have to pay child support.
"A Tim to Stand" - The Federation abandons Tim on Deep Space 9 in the hopes that he will be executed by the Dominion.
"Tim's Orphan" - Tim has long since vanished, but he leaves his teenage son on the O'Briens doorstep. O'Brien, still traumatized, wants nothing to do with the kid.
"Tim and Again" - Tim has used his time rift mastery to show up in the Delta Quadrant. Destroying a planet or two in the process. Whoops.
"Once Upon a Tim" - Naomi Wildman is warned of the dangers of Tim, who sneaks aboard the Voyager pretending to be a hologram (the usual way in).
"Timless" - Harry Kim crashes the Voyager into a planet, killing all onboard, in order to get rid of Tim. Getting the message, Tim reverses time and leaves in a huff.