This onion wont make me cry

Yeah, there 15 now-

*Deep inhale*
So, technically, there's one Doctor, however, that doctor regenerates whenever his body is harmed. Those different regenerations are portrayed by different actors with different personalities. So we've had 15 portrayals of the Doctors (16 including the War Doctor)

WAR DOCTOR?

Yeah, there was this thing called the Time War and the Doctor who was involved did some War crimes, y'know, the normal war stuff-

Time war?!

Wtf was the time war?

...
The more questions you ask the longer this would be-
The Time War was between the Time Lords of Gallifrey (which are aliens who look human and have the ability to regenerate.) and the Darlex (xenophobic aliens with metal armor that want to basically destroy everything)