John Richard Deacon (born 19 August 1951) is an English retired musician who was the bass guitarist for the rock band Queen. He wrote several songs for the group, including Top 10 hits "You're My Best Friend", "Another One Bites the Dust" and "I Want to Break Free"; co-wrote "Under Pressure", "Friends Will Be Friends" and "One Vision"; and he was involved in the band's financial management.

Deacon grew up in Oadby, Leicestershire, playing bass guitar in a local band, The Opposition, before moving to study electronics at Chelsea College, London. He joined Queen in 1971 on the strength of his musical and electronic skills, particularly the homemade Deacy Amp which guitarist Brian May used to create guitar orchestras throughout Queen's career. From the third album, Sheer Heart Attack, onwards, he wrote at least one song per album, several of which became hits. As well as bass guitar, Deacon played some guitar, keyboards and piano on Queen's studio work.

After the death of lead singer Freddie Mercury in 1991 and the following year's Tribute Concert, Deacon performed only sporadically with the remaining members of Queen before retiring from the music industry in 1997 after recording "No-One but You (Only the Good Die Young)". He has not performed on any of the other projects that the two remaining members, Brian May and Roger Taylor, have put together.

Deacon was inducted into the Rock and Roll Hall of Fame as a member of Queen in 2001 and into the Songwriters Hall of Fame in 2003.

John Richard Deacon was born on Sunday, 19 August 1951 at St Francis Private Hospital, London Road, Leicester to Arthur Henry and Lilian Molly Deacon (née Perkins). He had an older brother, Robert, who died aged 6 in July 1953 and a younger sister Julie, born in January 1956. John's father worked at the Norwich Union insurance company and in 1960 the family moved to neighbouring Oadby. Deacon was known to friends and his bandmates as "Deacs" or "Deacy".

Deacon took an interest in electronics at an early age, reading magazines on the subject and building small devices, including the modification of a reel-to-reel tape deck to record music directly from the radio. He studied at Linden Junior School in Evington, Gartree High School and Beauchamp Grammar School in Oadby, achieving eight GCE O level and three A level passes, all at grade A. He particularly enjoyed soul music.

In 1965, at the age of fourteen, Deacon formed a school band called The Opposition. The band would go through many lineup and name changes, with Deacon eventually leaving the band altogether in 1969 to pursue studies in Electrical Engineering at Chelsea College in London.

Deacon joined his first band, The Opposition, in 1965 at the age of 14. The band played covers of chart hits; Deacon played rhythm guitar using an instrument he bought with money borrowed from the group's founder, Richard Young. He switched to bass the following year after the original bassist was fired for not improving his playing as much as the other members. Deacon also acted as the band's archivist, taking clippings from newspapers of even the advertisements featuring The Opposition. After being in the band for four years, not long after the group cut an acetate of three songs, Deacon played his final concert with the band (then called The Art) in August 1969. He left as he had been accepted to study at Chelsea College in London (now part of King's College London), where he obtained a First Class Honours degree in Electronic Engineering in 1971. Having become a fan of Deep Purple, he saw the group perform the Concerto for Group and Orchestra with the Royal Philharmonic Orchestra at the Royal Albert Hall that September.