Tumblr question

i bought a domain

its fine i use a theme from other guy on my page? or is that wrong?

Does he own the theme? If so, it couldn't hurt to ask for his permission. If he say's no you can:

A) Respect his wishes and not use it

or

B) Rip the theme and use it anyways

It really comes down to whether or not you want to be "That Guy".