At some point during the Last Great Time War, the Doctor regenerated into this, his ninth incarnation. It is unknown at what point this happened. During the final battle of the Time War, the Doctor used a type of device (possibly a "Delta Wave") to destroy the Daleks, but it also destroyed the Time Lords. He was now the last Time Lord.
The Ninth Doctor has the same powers as all Time Lords. The Doctor's brain can handle and understand more information then most other species. The Doctor also has two hearts. The Doctor's senses are also very high.
The Doctor can survive much high levels of radiation then a human could.
He has a much higher stamina then that of a human.
The Doctor can regenerate at will. When wounded and about to die, he will do this. Regeneration will change his body, and even his personality. Yet, he will still remember his past, and is still the same person. This is The Doctor's ninth regeneration.
Doctor Who series 1 (season 27):