Dick Mills was in charge of sound effects and all the rest then, and he put the voice through a ring modulator or whatever gizmos he'd got at the time to make it sound a little more electronic.

He was though seen on-screen as the character Dugeen during the serial The Power of Kroll (1978–79). He also voiced K-9 for its return in the 2006 Doctor Who episode "School Reunion" then its cameo in the pilot episode of The Sarah Jane Adventures. Leeson however became frustrated himself with the limitations of the character and left the programme after the conclusion of the 16th season in 1978.

He was called back to do the voice of K-9 again for the 2006 episode "School Reunion" and again for the 2008 Doctor Who episode "Journey's End". He also played the voice of K9 in "The Sarah Jane Adventures" and the series "K9" and the TV pilot "K-9 and Company". John Leeson (born 1943 Leicester England) is a British actor who is best known for voicing K-9 on the television series Doctor Who from 1977 to 1979 and again in the 1980–1981 season.