5. With Himself
Of course arguably his greatest battle is with himself. He stands as a monument to change. Predominantly he's a sort of military man where his first eight incarnations tended to deplore anything of the sort. While he may have been hopeful that in throwing himself headlong into the Time War things would change in the name of peace and sanity, the very fact that the Eighth Doctor deliberately chose to make his next incarnation a soldier suggests that there could be an underlying residual trauma as to what he's doing and how he's doing it. While so far we've only seen the older and more wary War Doctor his younger self may well have sought out conflict in a bid to live up to his own billing. Which most likely means there's possibly blood on his hands beyond that of the children of Gallifrey if he chose to strap on Cass's bandolier and whizz off in search of people to save in his own militaristic way. Which would make the Tenth and Eleventh Doctors justified in their initial fear of him. After all, a reckless streak is one hell of a way to both announce and alienate yourself to your own kind, as the First Doctor, Meddling Monk, Master and Rani can all testify.