Warsmith
Warsmith (not to be confused with Warpsmith) is a rank/title employed by the Iron Warriors, given to the leaders of the legion's various Grand Companies. The Warsmiths each have a number of captains who in turn command a regular Company, placing the Warsmiths in positions akin to that of Chapter Masters. Warsmiths are highly skilled individuals, both in skill of arms and at siegecraft. They must also maintain a certain degree of savvyness amongst their equals and direct subordinates: if a Warsmith is killed by a fellow Warsmith, the victor might absorb his opponent's Grand Company, and a good number of Warsmiths obtained their rank by killing its previous holder. One of the most famous Warsmiths is Honsou, who has a great record in getting shit done.
It is interesting to note that the position of Warsmith can be held even when its holder is interred in a Dreadnought, assuming they don't go insane (well, too insane by Chaos Space Marine standards). An example would be Berossus from Graham McNeill's Dead Sky, Black Sun.
It's also interesting to note that every Warsmith other than Honsou tends to get killed after only one novel.