Gladiator

A gladiator was a type of fighter.

On Earth
In July 64, Ian Chesterton was once forced to fight Delos for the amusement of Caesar Nero in an amphitheatre. (TV: The Romans)

Murranus was a gladiator whom the Seventh Doctor and Mel Bush met in Pompeii before the eruption of Vesuvius destroyed the city on 24 August 79. (AUDIO: The Fires of Vulcan)

A World War I soldier from 1916 was sent to Rome in 97 by a Weeping Angel. The soldier found himself in the middle of a gladiator battle in the Colosseum. (COMIC: The Weeping Angels of Mons)

Elsewhere
A Shad'ath gladiator was one of the many creatures captured by the Zygon warlords, Anktra and Kestral. They planned to carry out a traditional duel on the planet Shontaa, involving fighting to the death using this variety of host bodies. This duel was observed, however, by the Fourth Doctor and Leela, who found the Zygon ship and freed the prisoners. (COMIC: Rest and Re-Creation)

The Doctor had acted as a gladiator "decades" before their thirteenth incarnation. (COMIC: Holiday Special)

Sometime after the thirteenth Doctor, Graham, Ryan, and Yaz had visited an alien amusement park (COMIC: Meet the Fam!), the team discovered that their individual memories of the visit had been tampered with to the point of being inconsistent with each other. Yaz's memory of the visit saw the Doctor being put into the park's gladiator games after winning a test of strength game. (COMIC: Holiday Special)