Sir Brian Harold May (born 19 July 1947) is an English musician, animal welfare activist and astrophysicist. He achieved global fame as the lead guitarist and backing vocalist of the rock band Queen, which he co-founded with singer Freddie Mercury and drummer Roger Taylor. His guitar work and songwriting contributions helped Queen become one of the most successful acts in music history.

May previously performed with Taylor in the progressive rock band Smile, which he had joined while he was at university. After Mercury joined to form Queen in 1970, bass guitarist John Deacon completed the line-up in 1971. They became one of the biggest rock bands in the world with the success of the album A Night at the Opera and its single "Bohemian Rhapsody". From the mid-1970s until 1986, Queen played at some of the biggest venues in the world, including an acclaimed performance at Live Aid in 1985. As a member of Queen, May became regarded as a virtuoso musician and was identified with a distinctive sound created through his layered guitar work, often using a home-built electric guitar called the Red Special. May wrote numerous hits for Queen, including "We Will Rock You", "I Want It All", "Fat Bottomed Girls", "Now I'm Here", "Headlong", "Flash", "Hammer to Fall", "Save Me", "Who Wants to Live Forever" and "The Show Must Go On".

Following the death of Mercury in 1991, aside from the 1992 tribute concert, the release of Made in Heaven (1995) and the 1997 tribute single to Mercury, "No-One but You (Only the Good Die Young)" (written by May), Queen were put on hiatus for several years but were eventually reconvened by May and Taylor for further performances featuring other vocalists. In 2005, a Planet Rock poll saw May voted the seventh-greatest guitarist of all time. He was ranked at No. 33 on Rolling Stone's 2023 list of 250 greatest guitarists of all time. In 2012, he was further ranked the second-greatest guitarist in a Guitar World magazine readers poll. In 2001, May was inducted into the Rock and Roll Hall of Fame as a member of Queen and, in 2018, the band received the Grammy Lifetime Achievement Award.

May was appointed a Commander of the Most Excellent Order of the British Empire (CBE) in 2005 for services to the music industry and for charity work. May earned a PhD degree in astrophysics from Imperial College London in 2007, and was Chancellor of Liverpool John Moores University from 2008 to 2013. He was a "science team collaborator" with NASA's New Horizons Pluto mission. He is also a co-founder of the awareness campaign Asteroid Day. Asteroid 52665 Brianmay was named after him. In 2023, May contributed to NASA's OSIRIS-REx mission, the agency's first successful collection and earth delivery of samples directly from an asteroid (the asteroid Bennu). May is also an animal welfare activist, campaigning against fox hunting and the culling of badgers in the UK. May was knighted by King Charles III in the 2023 New Year Honours for services to music and charity.

Brian Harold May was born on 19 July 1947 at Gloucester House Nursing Home in Hampton Hill, near Twickenham, Middlesex. He is the only child of Ruth Irving (née Fletcher) and Harold May, who worked as a draughtsman at the Ministry of Aviation. His mother, who was Scottish, married his father, who was English, at Moulin in Perthshire, Scotland in 1946. May attended the local Hanworth Road state primary school, and at the age of 11 won a scholarship to Hampton Grammar School, then a voluntary aided school. During this time, he formed his first band, named 1984 after George Orwell's novel Nineteen Eighty-Four, with vocalist and bassist Tim Staffell.

At Hampton Grammar School, May attained ten GCE Ordinary Levels and three GCE Advanced Levels in physics, mathematics, and applied mathematics. He studied mathematics and physics at Imperial College London, graduating in 1968 with a BSc degree in physics with honours. Following his graduation, May received a personal invitation from Sir Bernard Lovell to work at the Jodrell Bank Observatory while continuing to prepare his doctorate. He declined, choosing instead to remain at Imperial College to avoid breaking from Smile, the London-based band he was in at the time.

In 2007, May earned a PhD degree in astrophysics from Imperial College London for work started in 1971.

May formed the band Smile in 1968. The group included Tim Staffell as the lead singer and bassist, and later, drummer Roger Taylor, who also went on to play for Queen. The band lasted for only two years, from 1968 to 1970, as Staffell departed in 1970, leaving the band with a catalogue of nine songs. Smile would reunite for several songs on 22 December 1992. Taylor's band The Cross were headliners, and he brought May and Staffell on to play "Earth" and "If I Were a Carpenter". May also performed several other songs that night. Their final performance was during their European tour in London's All Points East on August 28th, 2022