The Doctor (aka Dr. Whooves/Hooves, Doc, Time Turner, Theta Sigma, or The Oncoming Storm) is a time-traveller currently residing in Ponyville. His time machine, the TARDIS, doubles as a residence for himself, River Song, his adopted son Tornado Bolt, and daughter Jenny.
The Doctor, currently, is a light tan Earth Pony with a quaffed brown mane and tail. His cutie mark is a running hour glass. He's a bit on the lanky side, but also seems rather in good shape for his age (Which he currently says is around 1100, but he's been known to round down significantly)
He is a rather curious pony, always watching the world unfold around him, and sticking his muzzle into situations he sometimes should have just avoided altogether. He tends to be rather friendly, like a crazy grandfather encouraging you to go out and have fun, regardless of what the other adults told you to do. Just... don't get on his bad side.
He can usually be seen sporting a bow tie, a purple jacket and vest, and the occassional stetson. (Because stetsons are cool now.)
He enjoys the taste of squash fingers and custard as a snack or treat.
Though he has access to many things beyond a pony's wildest imagination, the Doctor does his best to keep such things from leaving his home. He wishes to preserve the unique technological level of Equestria, without introducing things that don't belong there.
This section will focus on the Doctor's history in Equestria. For the Doctor's main history, go here at Tardis Wiki , and just put a pony spin on it
During his 8th regeneration, the Doctor took Celestia and Luna on an adventure across the universe just weeks before they took the throne. Though he brought them back mere hours after they had left. Since then, his travels have intersected with Equestria time and time again. If one looks closely, you can usually find a reference to the Doctor somewhere in the history books.
The Doctor's current stay in Equestria began in his 10th regeneration when the TARDIS crash landed in Ponyville after a freak temporal storm. His craft damaged and in need of repairs, the Doctor took up residence in the small town temporarily. He assisted Twilight Sparkle with the recovery of a meteorite, where he met Tornado Bolt, who had discovered the space rock. Learning that Bolt wasa runaway orphan, the Doctor took him in, and gave him a room in the TARDIS to stay. Eventually, after some encouraging from Princess Celestia, the Doctor adopted Bolt, promising the young colt that he would stay until a time Bolt no longer needed him around. Out of respect for the Princess, he has also promised not to take Bolt out of Equestria's system until the colt is old enough to make the choice himself.
After receiving messages from an old friend, the Doctor left Bolt in the care of Fluttershy and set off in the TARDIS, leading into the events that ended with him regenerating into his 11th incarnation, and the adventures with Amy Pond and Rory Williams that followed. The Doctor would soon return to Ponyville though, and after Princess Celestia confirmed his identity, settled back into the swing of things.
As is the case with the Doctor though, the universe once more called out for him, and the time pony set out again. This time seemed different though.. as his friends soon found out that there was a good chance he wouldn't be coming back. They also learned of Rule #1... the Doctor lies. Sure enough, the Time Pony returned, but he didn't return alone. Accompanying him back to Ponyville was a white mare with a blue book cutie mark by the name of River Song. River claims that she and the Doctor are married, despite the Doctor's arguments that it didn't count for reasons he has yet to explain. Regardless, the two now currently reside in the TARDIS, along side Tornado Bolt.
((For new players, be sure to check out: Rules for interacting with The Doctor))