Harry Houdini

Harry Houdini was a famous American magician and escapologist on Earth during the 20th century.

Biography
Houdini first met the Doctor in 1890, when the Doctor was in his first incarnation, although this was not their first encounter from the Doctor's perspective. At the time, the Doctor was accompanied by Ben Jackson and Polly Wright. Together, the four of them defeated the Ovids. At some point after this, Houdini met the Third Doctor, and travelled to the future with him and Jo Grant. (AUDIO: Smoke and Mirrors)

Between 1917 and 1920, Houdini, along with Sir Arthur Conan Doyle, publicly announced the existence of fairies following the release of the Cottingley fairy photos. Gwen Cooper believed this was all an act of self-publicity. (TV: Small Worlds)

In 1920, the Eleventh Doctor needed help defeating the Cuculus and decided to recruit Houdini during his act. When they were captured by the Cuculus, Houdini was easily able to break the locks holding him and the Doctor. After the Doctor defeated the Cuculus, they returned them to Earth and the Doctor returned him to his act. When people started getting sick, the Doctor realised that the Cuculus had infected them with a disease to wipe out humanity. Using a crystal from the Cuculus ship that Houdini had stolen, the Doctor was able to cure the disease. (PROSE: Houdini and The Space Cuckoos)

The Fifth Doctor, Adric, Nyssa and Tegan Jovanka later met Houdini when the Doctor answered a psionic distress call being sent from England in the 1920s. Unbeknownst to the Doctor and his companions, Houdini had been convinced by that the Doctor was evil. Houdini's relationship with the Doctor, already tense due to the Time Lord's refusal to offer the performer any clues as to his personal future (in particular whether he would ever be able to communicate with his deceased mother in the spirit world), became strained as a result of the incident. (AUDIO: Smoke and Mirrors)

The Eighth Doctor also met Houdini when he was travelling with Lucie Miller. Houdini taught Lucie how to escape from handcuffs during this time. (PROSE: The Great Escapes)

Behind the scenes
Houdini actually never investigated the Cottingly photos, despite some correspondence from Doyle that suggested he visit. Houdini was shown to be involved in the events in the 1997 film FairyTale: A True Story starring Paul McGann.