Moloch was the oldest and most powerful of the Elder Gods. He was the god of chaos, and according to legend he was born in "the fires of creation". (AUDIO: Protect and Survive) He was worshipped by humans before Christianity. (COMIC: Bêtes Noires & Dark Horses)
In the 20th century, two of Moloch's agents possessed several real life humans including Generals Petrov and Mitchell, in an attempt to prompt a nuclear war on Earth. However, these two were trapped inside a pocket universe of their own making, by the Seventh Doctor, who tricked them into inhabiting Peggy and Albert Marsden. The dimensional prison took the form of a ten-day time loop and only existed as long as the Elder Gods were trapped within it, preventing Moloch from freeing them. The Doctor meant them to understand what it was to live and die as mortal humans, and promised to release them once they could do this; however, they were left trapped for several hundred years, before Moloch saved them.
In the alternate timeline created by Moloch in the hope of destroying Earth, the militant hardliner Vladimir Kryuchkov became General Secretary of the Communist Party of the Soviet Union following the death of Chernenko in 1985 rather than the considerably more moderate Mikhail Gorbachev. On 9 November 1989, World War III broke out between the Soviet Union and the United States and its allies including the United Kingdom; given that nuclear weapons were used by both sides, hundreds of millions of people were killed in the conflict. This timeline was ultimately negated by the Seventh Doctor. (AUDIO: Protect and Survive)