Sir Brian Harold May (born 19 July 1947) is an English musician, songwriter, record producer, animal welfare activist and astrophysicist. He achieved worldwide 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", "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.