This may not be that new a question, but it's something I don't know. I undrstand the good Doctor is the last of his kind. The Time Lords all perished in the Time War. My question is if they're time travelers, why can't he go back to before they were all killed, or why hasn't he encountered any other time traveling Time Lords?
I'm sure there's probably an answer to this, but I'm not sure what it is. Thanks.
It's a Time War, throughout all of Time, and Gallifrey is Time Locked (IE: Frozen in Time, or out of Time)
As far as other Time Travelers, strictly speaking, The Time Lords never did approve of their race running wild throughout the Cosmos, so, there weren't many running around free, TARDISes are basically Gov't owned and pretty strictly regulated, it's not like every Time Lord has a TARDIS like we have cars, The Doctor stole his. Additionally, any Time Lords away from Gallifrey worth their salt, would almost certainly have run home to fight in the Time War. (Even the Master was lured in with a promise of more Regenerations if he helped in the War)