Count Grendel is the owner of Castle Gracht and the main antagonist of the Doctor Who episode The Androids of Tara.
He was played by Peter Jeffery.
Doctor Who - The Androids of Tara
Grendel wanted to be king of Tara. He took the rightful heir Prince Reynart prisoner to prevent him from being crowned, whereupon Grendel would be chosen to replace him. However, the Fourth Doctor used an android to substitute for the prince.
Grendel decided to force Romana, who was identical in appearance to Princess Strella, to marry Reynart. Grendel would then kill the king and marry his widow, becoming king. The Doctor arrived at the wedding and revealed the count's plot, challenging Grendel to a sword fight.
Grendel lost the fight, dived from the battlements of Castle Gracht into the moat and swam away. He was exiled by Reynart.