Sure, there's others with a very high degree of skill like Carmack, but it's his consistent ability to come up with amazing stuff over the last two and a bit decades that gives him legend status.
It's not just ability and skill, it's also impact on the industry (which, obviously, requires a degree of luck and circumstance). It sounds pretty hash, but it's kinds hard to be considered a legend/god/whatever if no one's heard of you.
But you raise an interesting point. For those people how do make an impact, to what degree is it due to circumstance, and to what degree their own skill? There's loads of very highly skilled people in any given field, and yet only a very small number of them will ever make much of an impact on that field. Why is this, and what differentiates the ones who do from the ones who don't?