Marotin Harkonnen

Marotin Harkonnen is the son of Dmitri and Daphne and the older brother of Abulurd. He was mentally challenged, an embarrassment to the family, and he died at the age of 28.

Behind the Scenes
In The Dune Encyclopedia Vladimir and Abulurd are descibed as having a retarded brother named Araskin, and he is Vladimir's full-brother by his mother Muertana Sarobella, instead of his half-brother by a concubine of his father.