The Spectre of Lanyon Moor
Sancreda was a Tregannan who became stranded on Earth during a geological investigation after supposedly being abandoned by his brother Scryfan in circa 16000 BC. He invaded the minds of many in Lanyon Moor, including Mrs Moynihan, and forced them to do his bidding. With his psionic powers, he was able to completely destroy Sir Archibald Flint, Philip Ludgate, Professor Morgan and Moynihan herself.
He was finally killed by Brigadier Lethbridge-Stewart after threatening to destroy Earth in 2000. (The Spectre of Lanyon Moor)