If you watch Escape from New York, you'll notice how similar David Hayter and Kurt Russel's characterizations are, too. I don't know if that was a conscious thing on Hayter's part, or if the director/casting director pushed him in that direction.
The characters in Metal Gear have been based on various actors over the years. As someone pointed out, Snake was originally inspired by Michael Biehn's character in The Terminator. In Metal Gear 2, he became Mel Gibson after Kojima saw Lethal Weapon:
And Big Boss's inspiration in that game was fairly blatant...
It wasn't until Metal Gear Solid that Kojima really got the confidence to do his own thing rather than an amalgam of famous movies and movie characters, although obviously the inspiration was still there. Apparently Snake's face in that game (which has become his modern image) was based on Christopher Walken, though I don't really see the resemblance much.
