Mortarion

Mortarion is primarch of the Death Guard, a poison-world warlord who hated psykers and still became a daemon prince of Nurgle. He wanted to prove a man could beat a toxic sky with will alone. The god of rot found that funny.

Typhon trapped his fleet in the Warp until he accepted the plague god's gift. Barbarus is gone. The Plague Planet is what he has left. He brought that gift to Ultramar in the Plague Wars and still could not keep Guilliman dead.

He resents Typhus, resents the Emperor, and resents that endurance became slavery. Nurgle does not mind. Endurance is the point.