John Francis Christopher Ducker, known professionally as John Leeson, is an English actor. He is known for portraying Bungle in Rainbow and voicing K9 in Doctor Who and spin-offs The Sarah Jane Adventures and K9.

Rainbow is a British children's television series, created by Pamela Lonsdale, which ran from 16 October 1972 until 6 March 1992, made by Thames Television. The series was revived by Tetra Films from 10 January 1994 until 24 March 1997, in two different formats from the original Thames series, with differing cast members.