William (Gone Fishing)

William, also known as Isaac, was a companion of the Sixth Doctor who created a musical composition that became a deadly weapon. (PROSE: Resonance)

Biography
William first met the Sixth Doctor in a fishing shop, where the Doctor proposed to take William on a fishing trip. William accepted and the Doctor took him to the far future where they entered a fishing competition with a group of future-humans. William travelled with the Doctor in the TARDIS after the competition had ended. (PROSE: Gone Fishing)

The Eighth Doctor travelled back in time and prevented William from joining the Sixth Doctor on the fishing trip, and gave him a recorder instead, telling him to "try something else" other than fishing. (PROSE: DS Al Fine)