Mine was probably...
Experiment 2.0. He has changed MUCH since his creation... Even his physical features!
See, he was my first character, and began as a full on mutant, with dark powers and spike powers, along with a little skill at making his own costumes, hence why it was so ragtag- A white tank top, ring shoulders, jeans, and boots. Also, some goggles for better withstanding of battle.
He is 5'2" in-game, but I RP him as around 6'4".
Why the height difference?
It's actually pretty funny- When I started the game, it was on an old laptop, and I couldn't make anyone even average height because he glitched up the graphics. I don't know why.
Eventually, he shifted from full Mutant, to having some skills in technological creations. Note, this was before Issue 1 even, so no Icon, no nothing.
I RPed him first in Whitemoore, and I was, what, 13? I was terrible at it. I had no idea what grammar WAS, let alone how to use it, and failed miserably otherwise.
(How I became a Grammar Nazi in, like, a year I'll never know.)
Eventually, he shifted to Super-Hero, tights, tech power pools, flight, all that stuff. He THEN shifted into the more modern 2.0. Red Metallic armour, cape, goggles, dirty blonde hair, sarcastic and humorous nature, and generally very heroic.
Although, I HAVE shifted his suit a bit recently... I'll post pictures soon enough, but he just looks much cooler now, both in his 'Experiment 2.0' costume, and his 'Time-Travel' costume.
Yes, I actually made a time-travel costume. Oh, and his Civilian Suit is much cooler now too. Less monotonous.
Sikk.
Sikk was supposed to be a throw-away concept. Just some gothed-out loser kid with powers beyond his comprehension.
Then I got to thinking about where those powers came from.
Now I've accidentally injected some of my nightmares into it, and I don't entirely have a handle on where this thing is going.
My Stories
Look at that. A full-grown woman pulling off pigtails. Her crazy is off the charts.
A few of my characters have taken off on their own from how I originally created them. The two you all would be familiar with would be Brutish Ghoul and Solid Shot.
Solid was my first successful hero after the debacle that was my fire/fire tanker. He started out as a grim, somewhat emotionless android who had only come to Paragon City because of a glitch in his programming during a relatively normal upgrade. The glitch in his WinBot 2000 was the beginning of the humor that would slowly creep in and take Solid over around the time I started posting on the board and met Essex and Hal.
Almost overnight the grim security bot became an almost agressively funny droid who had come to be what he was through a series of amusing, almost laughable incidents. The glitch during upgrading his WinBot OS stuck around but was added onto by a personality program written by a Korean prodigy which has contributed endless lulz. Then came the realization of how his electricity manipulation powers were actually from modified Rikti tech and how that single realization enabled me to construct almost all of his life before he came to Paragon.
From being simply the best character to play around in CoH with, Solid became an extension of the more sarcastic and sociable side of my personality. He's mirrored by Toy Dispenser, who seems to be mostly influenced by the logical and anti-social side, though both androids have their moments in the other extreme. It was very interesting to see how that came about.
And then there's Brutish Ghoul.
Originally created by my little brother as his first brute, Ghoul was named because my brother always took the name Noxious Ghoul as his user ID. Brutish came about when I suggested a suitable adjective for a brute named Ghoul. My brother left Brutish Ghoul behind when he reached level 30 and left for WoW. I took over the character and gifted him with a very stereotypical personality. He was little smarter than his name suggested and loved to fight simply for the sake of fighting.
Somewhere along the way I got it into my head that Ghoul wasn't actually undead. I attribute this to the time in Final Fight when Ghoul was 'killed' and for some reason I had him collapse into a pile of black ooze that tried to eat everything around it. As with most of my characters, serious development happened as I started trying to figure out why that had happened, why Ghoul was like he is, and why he seemed undead but isn't.
Along the way he got smarter, I learned he fought because it was how he gained sustenance, and why his powers worked the way he did. Out of all of him, I think it was the odd combination of Dark Melee and Invulnerability that made my mind really churn with ideas. One of these days I'll have to thank my brother for giving him those power sets.
Then there's also Balsk and Toy's bots, but I think I'll save those for later.
Statesman said let there be heroes, and there were heroes.
Lord Recluse said let there be villains, and there were villains.
NCsoft said let there be nothing, and there was nothing.
*Grins*
All of my characters except for my most recent creations.
Seriously, just about all of them. When I started here I was...a bit of a jerk. I didn't think before I posted and I didn't listen to the advice of others. Since then I've changed the few characters I'm still using from there.
Darkvapor, for instance, was originally a magic overlord type. He's now a super intelligent symbiote that lives inside human hosts. He also completely detests magic now.
Radiator was originally a complete psychopath that liked to attack people for no reason. Now he's a much more calm and reserved character.
I think I can safely say that these changes were all for the better.
Most of my DWC characters have completely flipped my head over backwards. Kaega was originally a wise cracking street fighter who liked throwing around a baseball bat. Now He is a natural immortal with a self aware sword that contains the bloodlust of every battle it's been through. . .go figure.
And Justice Reborn. He was originally a mutant energy weilder. Now he wears a clothlike tech suit that gives him a boost in strength and reflexes. It's weird. Mutant NRG/NRG blaster to Tech MA/SR Scrapper.
I do not know my reasons for posting, but post I must. ~~Build
"We can't stop here, this is bat country."
--Johnny Depp
"I ain't bi-curious, I'm a man. Why do you think I'm wearing this tight spandex and got all these muscles?" Meatwad
I'm pretty much the reverse of DV, most of my recent characters have been remade multiple times.
Then there's my 8' tall half demon 
El D never really had a direction to begin with. He was just a character, powerset, and costume that I thought was cool. Heck, while he was in the Shadow Manor, his current bio was nonexistent. Now I've got a (kinda) built up back story for him, and a future story as well (albeit mostly in my brain, not typed up yet).
Other than that, I've had about two or three characters that have morphed away from what I originally intended, and I'm working on one character now who's a combo of three different other concepts and who's had 3 remakes in-game already.
Global - @El D
Servers - Protector
So... we have a fair number of experienced RPers here, and I'm sure that at least some of you have had the odd experience of having a character completely jump the rails and develop naturally in a wildly different direction than you expected, to the point that you're wondering just who's in charge here.
So, considering that... I was just wondering- what's the fastest you've had a character hop the tracks and go wandering off in a direction you really hadn't planned? For me, on the CoH boards, it would have to be Target Lad, who was originally simply a sly nudge-nudge wink-wink at the "Robin, the Boy Hostage!" era of barely-teen sidekicks. By the time I started posting with him, he had become aware of his position as the "Hey, listen, you wear this brilliantly-coloured costume and go stand in the brightly-lit open while I wear all dark colours and hide in these convenient all-concealing shadows while we wait for the villain" kid, and, while not able to do a lot about it, sarcastically resented it.
But the grand bull-moose winner for me would have to be one on another board that spun wildly out of control to the point that he barely resembled the original concept... during the writing of his bio.
He was originally intended to be a rather grim character, unhappy with his lot and fighting the system as an air pirate in a dystopian future- somewhat akin to Rick Blaine in Casablanca in personality. By the time his bio was done, he had mutated into a deranged, hyperactive pastiche of Don Karnage, Max Sterling, Captain Jack Sparrow, human-form Greebo, and even a bit of Miles Vorkosigan, completely batty and considerable fun to write. Kind of a shame that the RP site I played him on closed down so quickly, and that I haven't been able to wedge him in anyplace else :/
"A soft answer turneth away wrath. Once wrath is looking the other way, shoot it in the head." Seven Habits of Highly Effective Pirates
MA Arcs: #12285, "Small Fears", #106553, "Trollbane", #12669, "How to Survive a Robot Uprising"