Gareth was a security guard at the Institute for Technological Advancement and Research in San Francisco on 31 December 1999.
While on duty he encountered the Eighth Doctor and Grace Holloway after the Doctor had stolen a piece from the beryllium atomic clock that was to be unveiled at midnight. The Doctor immediately recognised Gareth and urged him to answer the second question on his midterm exam because if he attempted to answer the third question he would get it wrong. When Gareth demanded to see what was in the Doctor's hand, the Doctor showed him a jelly baby, which Gareth ate.
The Doctor explained to Grace that, in 2009, Gareth would head the seismology unit of the UCMA taskforce and invent a system for accurately predicting earthquakes. Gareth's system would be credited for saving the human race several times. (TV: Doctor Who)