Ralph Hubert "Sonny" Barger Jr. (October 8, 1938 – June 29, 2022) was an American outlaw biker who was a founding member of the Oakland, California charter of the Hells Angels Motorcycle Club in 1957. After forming the Oakland charter, Barger was instrumental in unifying various disparate Hells Angels charters and had the club incorporated in 1966. He emerged as the Hells Angels' most prominent member during the counterculture era and was reputed by law enforcement and media to be the club's international president, an allegation he repeatedly denied. The author Hunter S. Thompson called Barger "the Maximum Leader" of the Hells Angels, and Philip Martin of the Phoenix New Times described him as "the archetypical Hells Angel", saying he "didn't found the motorcycle club ... but he constructed the myth". Barger authored five books, and appeared on television and in film.

Barger served a total of 13 years in prison, following a conviction for heroin trafficking in 1974, and a 1988 conviction for conspiracy to bomb the clubhouse of a rival motorcycle club, the Outlaws. He was also acquitted of murder in 1972, and of racketeering in 1980. Barger rejected accusations from law enforcement characterizing the Hells Angels as an organized crime syndicate, and maintained that the club should not be held accountable for crimes committed by individual members.

Ralph Hubert Barger Jr. was born in Modesto, California, on October 8, 1938, the son of Kathryn Carmella (née Ritch) and Ralph Hubert Barger. His father had German and Dutch ancestry, and his mother was of Italian descent. His mother left the family when Barger was four months old, leaving him and his older sister Shirley to be raised by their Pentecostal grandmother and alcoholic father, a day laborer on the Oakland docks. Barger grew up in Oakland in the post-war era, during which time the city's shipbuilding and automobile industries went into decline, leading to a significant rise in unemployment.

Growing up, Barger was suspended from school several times for assaulting teachers, and he often fought with other boys. He dropped out of school in the tenth grade. Although many of his school friends became drug addicts, Barger worked at a grocery store and enlisted in the U.S. Army, aged sixteen in 1955. He was given an honorable discharge fourteen months later when it was discovered that he had forged his birth certificate in order to be able to join. Barger had liked the discipline, masculine camaraderie, and learning how to disassemble weapons. After his return from the Army, Barger drifted between menial jobs and lived with his father in a single residence at a hotel, later moving in with his sister and her children.

In 1956, Barger joined his first motorcycle club, the Oakland Panthers, which he founded with a group of fellow military veterans. After that club disbanded, he started riding with another group of bikers, one of whom, Don "Boots" Reeves, wore a patch that belonged to a defunct Nomads chapter of the Hells Angels in North Sacramento. Founding their own Hells Angels club on April 1, 1957, each member wore the patch – a small skull wearing an aviator cap set within a set of wings, later copyrighted as the Hells Angels' "Death's Head" logo – after having replicas made at a trophy store in Hayward.

Barger was not the founder of the Hells Angels as is often claimed – the group was founded in 1948 – but he became its best known member to such an extent that he is often misidentified as the club's founder. He and the Oakland Hells Angels were initially unaware that there were several other, loosely affiliated clubs using the same name throughout California. The founding members of the Oakland Hells Angels were "basically honest blue-collar or unskilled workers looking for excitement", according to George "Baby Huey" Wethern, who became the chapter vice president in 1960. Unlike the World War II veterans who formed the early Hells Angels chapters, many of the founding members of the Oakland chapter were former servicemen with disreputable military records. Barger described his chapter as a "wild bunch".

After a chance encounter with a member of a pre-existing Hells Angels chapter, Barger learned of the club's history, rules, regulations and procedures. He was appointed president of the Oakland chapter in 1958 following a series of meetings with Hells Angels from Southern California. With Barger as president, the Oakland Hells Angels traveled around California and amalgamated with the other Hells Angels chapters, dividing territory and forming club bylaws. While infighting did occur between the chapters, conflicts predominantly arose with other clubs such as the Gypsy Jokers.

When Otto Friedli, the founder of the original San Bernardino Hells Angels chapter, was imprisoned in 1958, Barger was proclaimed de facto national president. One of his first actions was to relocate the club's "mother chapter" – the national headquarters – from San Bernardino to Oakland. Later that year, Barger suffered a fractured skull during a fight with Oakland police. Although the basic organization was in place when Barger assumed leadership of the club, he introduced additional rules pertaining to new members, club officers, and the establishment of new chapters. Under Barger's leadership, the club's membership began to increase. By 1960, the Oakland Hells Angels had established an extensive narcotics network within the club. Some of Barger's rules included "no using dope during a meeting" and "no drug burns" (rip-offs). The Hells Angels worked as "part-time distributors" of drugs in the 1950s and early 1960s.