Blight-master (a rank akin to Chapter MAster, Apostle, etc.) Task Tak leads the hordes of Nurgle in the Calixis sector.

This venerable Astartes is birth-brother to Sis Tak, the venerable dreadnought that serves Castor (the fact is not widely known, but Castor sees and hears many things). For two Terran borthers to both become marines, let alone marines of two different Legions is very rare indeed. If there were others they are almost certainly long gone by now, making the Tak brothers something unique.