Saul Hudson was born in Hampstead, London, on 23 July 1965, but raised in Blurton, a small suburb in Stoke-on-Trent, until age 6, before moving to Los Angeles, California. He was named after cartoonist Saul Steinberg. His mother, Ola J. Hudson (née Oliver; 1946–2009), was an American fashion designer and costumier. His father, Anthony Hudson, is an English artist. Although there has been speculation, Slash has refuted the claims that his father is Jewish. Of his mixed background, Slash has remarked, "As a musician, I've always been amused that I'm both British and black; particularly because so many American musicians seem to aspire to be British while so many British musicians, in the '60s in particular, went to such great pains to be black."
During his early years, Slash was raised by his father and paternal grandparents in Stoke-on-Trent while his mother moved back to her native United States to work in Los Angeles. When he was around five years old, he and his father joined his mother in Los Angeles. His brother, Albion "Ash" Hudson, was born in 1972. Following his parents' separation in 1974, Slash became a self-described "problem child". He chose to live with his mother and was often sent to live with his beloved maternal grandmother whenever his mother had to travel for her job. Slash sometimes accompanied his mother to work, where he met several film and music stars. He was given the nickname "Slash" by actor Seymour Cassel because he was "always in a hurry, zipping around from one thing to another".
In 1979, Slash decided to form a band with his friend Steven Adler. The band never materialized, but it prompted Slash to take up an instrument. Since Adler had designated himself the role of guitarist, Slash decided to learn how to play bass. During his first lesson, Slash decided to switch from bass to guitar after meeting Robert Wolin, a teacher at Fairfax Music School, and hearing him play "Brown Sugar" by the Rolling Stones and a Cream song. As a result, Slash stated, "When I heard him do that, I said, 'That's what I want to do.'" Equipped with a flamenco guitar given to him by his grandmother, he began taking classes with Wolin. He vividly recalls the feeling after learning "Come Dancing" from Wired by Jeff Beck, which he described as "fucking awesome".
A champion BMX rider, Slash put the bike aside to devote himself to playing guitar, practicing up to 12 hours a day. Slash attended Beverly Hills High School and was a contemporary of musicians Lenny Kravitz and Zoro.
