In series three of Game of Thrones Brandon Stark is revealed to be a Warg. Jones tells him that he is the only Warg he has ever seen to be able to control humans. Even to date we have only ever seen him control Hodor. Granted, Hodor is strong but there are times when it would have been better to controls someone else. So I was wondering if he actually can controls anyone else or can he only control Hodor because he is (to put it in Theon's words) a half-wit? Or does it have something to do with the fact that he has Giants blood and is therefore not technically human but a hybrid?
Based on the books, there is a chapter about another Warg who is a Wildling, and he is attacked by white walkers and tries to possess a woman he is with in order to escape.
However, in order to fully possess her he has to destroy her consciousness and inhabit her body himself, but her mind fights back and they both end up being killed by the white walkers.
I think that Bran is able to possess Summer so easily from the start because he has a close connection with his Direwolf, and rather than destroying the consciousness he more or less moves it to the side and takes over control of the body, and when he is finished Summer's consciousness moves back.
It will be a similar thing with Hodor. Whilst not being a lesser animal like a wolf or a bird, he is not quite a fully functioning human either. This along with the closeness Bran has developed with him, when Bran Wargs into Hodor's mind he understands it is Bran's consciousness and allows him to take over, as he knows Bran is not going to crush his mind and permanently possess his body.
So Bran might be able to control the bodies of other people he is close to, as they will know it is his mind and will likely trust him to possess their body, but it would be such a foreign thing to happen that most people, even those who trust him, would likely fight back on instinct and not allow him to possess them.
Hodor does not quite have the capacity to do this, as he is, to quote Theon, "a half-wit".
Although it is also stated that Bran is a particularly strong Warg. With enough training, he could probably crush any but the most strong-willed person's consciousness.
He also controls his direwolf, Summer. We've seen that in the TV show. As far as humans go, it is believed that being a Warg will also allow him to jump into other people. However, he has not done so in the TV show, or in the books, so warging into a person other than Hodor is pure speculation at this point.