Oliver was a twitcher when he was young. (AUDIO: The Cold Equations) At school, Oliver held the status then known as "fag", meaning he performed menial tasks for older students. (AUDIO: The Perpetual Bond) Whilst he studied mathematics, he did not consider himself especially good at it. (AUDIO: The Cold Equations)
Oliver became a city trader in London, a job that he enjoyed. (AUDIO: The Perpetual Bond) By 1966, he had fallen in love with Georgie. In that year, the Metropolitan Police Service questioned Georgie, who admitted the relationship (AUDIO: The First Wave) and thus left Oliver facing arrest himself. This panic meant that he was able to perceive the true form of the Fulgurites, whom he helped the First Doctor and Steven Taylor defeat before asking to join them in the TARDIS, seeking to escape the police as he felt his life was over. (AUDIO: The Perpetual Bond)
He initially kept his sexuality from the Doctor and Steven, as he believed that they would disapprove and force him to leave the TARDIS if they were to find out. After he had confessed his secret, though, Steven assured Oliver that the Doctor would do nothing of the sort. Furthermore, Steven told him that by his time, there was no longer any stigma attached to homosexuality and that same-sex relationships were common. Upon learning of Oliver's sexuality the Doctor said the crime was society's, not Oliver's. (AUDIO: The Cold Equations)
He travelled to the planetoid Grace Alone as the Doctor saw in a database that they had been there. He was killed by the Vardans but remained as a ghost in the TARDIS. As a ghost, he witnessed the Doctor's regeneration into his second incarnation in Antarctica in December 1986. (AUDIO: The First Wave)
Oliver was polite and had a strict moral code resulting from his upper-class upbringing. (AUDIO: The Perpetual Bond) He kept his sexuality a secret and feared that Steven and the Doctor would reject him once he divulged it. He blamed himself and his running from his problems on Earth for his death. (AUDIO: The First Wave)
Behind the scenes
From an in-universe point of view, Oliver is[update], chronologically, the earliest known non-heterosexual human companion of the Doctor.