Isambard Kingdom Brunel

Isambard Kingdom Brunel was a renouned 19th century engineer and — in the words of the Eighth Doctor — "the man who built the modern world".

Brunel designed the Clifton Suspension Bridge, the SS Great Britain, the Thames Tunnel, the Tamar Bridge and Paddington station. He also made significant contributions to the Great Western Railway.

At some point, one of the first five incarnations of the Doctor met Brunel and acquired his business card, which he kept in his address book. (TV: The Two Doctors)

The Sixth Doctor met him in 1828 in one of his father's tunnels. He helped the Doctor investigate something strange in the tunnels and came through a strange city under the river. He came with him and encountered Rispa. He stole the TARDIS key and wanted to pilot the TARDIS away. (AUDIO: Iron Bright)

Madeline de Roche speculated that the Eighth Doctor's TARDIS was a new design by Stephenson or Brunel. (AUDIO: Other Lives)

In Juliet Kemp's home, the ghost of Isambard Kingdom Brunel was trapped inside a tea cosy. (PROSE: Contributors)

Alternate timeline
As part of the Eternines' plan to alter history and drain Earth of energy to sustain their own world, their agent Jared Malahyde offered Brunel vital assistance in constructing his major projects in 1831, resulting in Brunel completing the Clifton Suspension Bridge much earlier. The Eighth Doctor, Fitz Kreiner, and Anji Kapoor met Brunel in 1843 and saved him from the Cleansing; afterwards, he was taken into the future that would result from these events, and he sacrificed himself to give the Doctor a chance to undo the changes to history. This erased his memories of the Doctor. (PROSE: Reckless Engineering)