Michael Newman was a human from 20th century Jamaica. He had latent psychic powers, even though he ignored it.
He and his wife Audrey came to England in the 1950s: she went first with their new-born baby, Josetta, and he followed some time after. As he was going, he fished out from the ocean a strange piece of dark red rock, which he decided to bring to his wife as a present. In reality, the rock was the knot-heart of a race of anemone changelings, parasite creatures able to morph into other life species. They were awakened by Michael's powers, took control of his mind and created a copy of him; then, they imprisoned him and placed the knot-heart on his chest. This would have kept him alive and conscious, so that they could go on exploiting his mind as an energy source for their morphing abilities.
His duplicate disembarked in London and reached Audrey and her uncle, Joseph Roberts, pretending to be Michael. He found a work at the London docks and started directing the operations of capture and replacement of other human beings. When the TARDIS crashlanded as a result of the changelings creating a psychic connection to it, Joseph sheltered Steven Taylor, Sara Kingdom and a comatose First Doctor in the house where he lived with the humans. That same night, Michael and the other duplicates kidnapped the Doctor and the TARDIS, intending to use it as an alternative and more powerful energy source.
For the next two weeks, the false Michael worked with Steven at the London Docks, and even shared with him his fare to help him for the first time. In turn, Steven defended him when a group of racist co-workers, led by Billy Flint, picked out on him; however, his intervention caused a fight, and both Steven and Michael were fired. That night, when Flint and others came to assault the Newmans' house, Michael called the crowd of changelings and had them kidnapped and taken to the docks. Steven followed them and found out the truth, and Michael then had him captured and copied; he did the same thing to Audrey too, when she arrived not much later.
Together with Steven and Audrey's duplicates, Michael went back to the house to take Josetta, but Sara recognized it was a fake and run away. Then, instructed by the Doctor (awaken by Steven from his coma), she went to the dock and awoke the original Michael. Being conscious and aware all the time, he had understood how it was possible to beat them, and told Sara to take the knot-heart and throw it back into the sea. When Sara did that, he stayed behind to fight against Audrey's duplicate, thus allowing her to destroy the knot-heart.
Later, the Doctor visited Michael to look on his conditions. Unlike the other prisoners of the changelings, who were in a coma, Michael was going to remember what happened; for the rest, though, the man was in good health. The Doctor then saluted him and praised him for what he did, and for how he kept fighting against the changelings' influence all that time, to save his family. (AUDIO: An Ordinary Life)