Colonel Radec is "The Dragon" in Killzone 2. As far as I know, he hasn't appeared in any other game.
But what's even more funny is how no one is surprised by this. In Killzone, the Helghast ARE the main characters. Oh sure, you play as the ISA and the Helghast are who you fight. But the Helghast are much more fleshed out and the Colonel Radec fight is one of the most memorable things about it.
But he has only appeared in one out of four games and even then he's not in it much. But Radec made so much of an impression in easily the series' best game that of course HE would be picked to represent the main characters of the universe.