Harry Houdini

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

Biography
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.

This was Houdini's first encounter with the Doctor, but not the Doctor's first encounter. An earlier Doctor would visit Harry later, where he would learn how Houdini did all his tricks. (PROSE: Houdini and The Space Cuckoos)

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 Conan 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.