Ghengis kahn pronunciation?

I have a friend who loves mongolian history (I think that's what he's interested in. Weird subject; kind of off the track). Anyway, somehow today our conversation ended up on the military leader Genghis Khan. I pronounced it Gaingis (with a G sound), and he told me it was actually pronounced Jaingis (with a j sound). I disagreed, having always heard it pronounced with a g, and we got into an oddly heated argument for a subject I don't particularly care for. Anyway, how is it pronounced?