I know there is already a citation being called for but this "Mortarion, already a close friend of his brother's, was too easily persuaded, having been turned long before the Heresy through the efforts of his first captain Calas Typhon." Has no legs. The IA , I believe, states that Mortarion and his legion minus Typhus turned after they became stranded in the warp. And that was after the Istvann massacre IIRC