Mordred is the secondary antagonist of the Doctor Who story "Battlefield".
He was portrayed by Christopher Bowen.
Mordred was the son of the immortal sorceress Morgaine and a fellow immortal from a dimension where the Arthurian legends were fact. He travelled to Earth's dimension with a small party of troops in response to the call of Excalibur and engaged in a running battle with Ancelyn, a knight from his own dimension with whom he had a long history. When he eventually caught up with Ancelyn, he recognised the Doctor as Merlin, as Ancelyn had done, and the Doctor was able to bluff him into retreating.
Mordred next summoned Morgaine and together they planned to retrieve Excalibur from King Arthur's resting place. However, on discovering a war memorial, Morgaine told Mordred he had brought dishonour on them by fighting on the locals' land without showing respect for their dead and sent him from her presence. He took refuge in the Gore Crow Hotel, indulging in ale and ignoring the threats of UNIT's Flight-Lieutenant Lavel, until Morgaine retrieved him.
Mordred led Morgaine's troops into battle against UNIT near the site of the Salamander 6-0 nuclear missile they were transporting. The Doctor arrived and tried to halt the fight, at which point Mordred revealed it was merely a diversion to allow Morgaine to retrieve Excalibur, which the Doctor had left with Ace and Shou Yuing. The Doctor threatened Mordred with a sword unless Morgaine, who was viewing events telepathically, stood down but Mordred knew the Doctor would not kill him in cold blood. The Brigadier stepped in with the same threat but Morgaine simply told Mordred to die well. The Doctor and the Brigadier took Mordred prisoner but he managed to slip away and join Morgaine as the Doctor recovered Excalibur.
Although they apparently returned to their own dimension, Morgaine and Mordred in fact took control of the Salamander 6-0, threatening to detonate it. Mordred fought Ancelyn while the Doctor confronted Morgaine. Mordred triumphed and prepared to despatch his opponent but was knocked unconscious by the Doctor, who instructed UNIT's Brigadier Bambera to take him and Morgaine into custody.