William George "Jock" Ross (born 5 August 1943) is a Scottish-born Australian outlaw biker, best known as the founder and the "Supreme Commander" of the Comanchero Motorcycle Club and for his involvement in the Milperra massacre of 1984. Ross was sentenced to life imprisonment with Judge Roden childing him as one of the men most responsible for the shoot-out at the Viking Tavern.

Ross was born in Glasgow, Scotland into a working-class family. Ross grew up in the Gorbals neighbourhood of Glasgow, where his father worked as a lorry (truck) driver. Ross stated of his youth: "In the old Glasgow days you never backed off, that’s how you survived. The Gorbals was tough and you had to be tough too." He served in the British Army in the Royal Engineers. Ross joined the British Army at the age of 17 and served for 7 years. As an engineer, he was involved in clearing minefields left over from the Second World War in Libya as well as laying minefields in the Aden Protectorate (modern Yemen) and Hong Kong. After his honourable discharge, he settled in Australia, making his home in New South Wales. In 1966, he settled in a coastal flat and then moved to Point Clare. Ross-who was known to his friends as "Jock" instead of William-worked variously as a lorry driver and as an apprentice blacksmith.

Ross befriended a number of Australian veterans of the Vietnam War, saying in a 2019 interview: "I came out of the army, came here. People come out of the army, especially soldiers coming back from Vietnam back in the '70s, the late '70s … they came, and they were treated like lepers … not real good. Me, as an ex-soldier, I empathised with them". Ross founded Comanchero Motorcycle Club in 1968 with the name being taken from a 1961 John Wayne Western film The Comancheros that Ross adored. The Australian journalists Lindsay Simpson and Sandra Harvey described Ross as a natural "leader of men", an extremely charismatic man whose machismo and toughness inspired much devotion from other men. In 1971, Ross purchased a property along the then rural Mangrove Mountain Road for $800 that became his home. Settling with Ross in his caravan were his first wife Sandy and their infant daughter Deidre. Ross found the sunny New South Wales countryside to be a refreshing change from the decaying industrial neighbourhoods of the Gorbals where he had grown up. Ross's only major weakness was that he believed in ghosts, and was terrified of the spirits that he believed wandered around the New South Wales countryside at night. In particular, Ross was convinced that his caravan was haunted by the ghost of a 19th century gold prospector who had drowned in a nearby creek along with the ghost of a lorry driver who had crashed on a highway close to his home.

Ross had known a number of motorcycle riders who liked to drink in the pubs along a coastal road north of Sydney and persuaded them to join the Comancheros. Ross led the Comancheros in series of brawls against another outlaw biker club, the Knights over the course of 1973. In May 1973, Ross executed an ambush of the Knights when he sent an emissary to the Tall Timbers Hotel in Ourimbah to say that Ross and a few other Comancheros were having a keg party out in the bush. When the Knights arrived at the party, Ross along with the entire Comancheros were waiting for them and carried out the ambush that Ross had carefully prepared. During the course of the fight, Ross was run over by a Knight in his motorcycle, breaking his leg and causing him to have a slight limp thereafter. Ross continued his feud with the Knights by laying in wait for them along in the bushes along the coastal roads and he would try to shoot them with his rifle when he saw them. Simpson and Harvey wrote: "Jock Ross had by then built an aura around himself. Even the police with whom he had his earliest dealings spoke of him with respect. He was the sort of man the police admired, a man with a fearsome reputation, someone to be reckoned with". That Ross beat up a "pug" (a professional fighter) in a bar brawl contributed to the respect that the police felt for him. In response to a warning from Sergeant Max Lamond of the Newcastle police that his feud with the Knights was getting out of hand, Ross relocated the Comancheros to the Sydney suburb of Parramatta. Ross hung a sign on the wall of the Comancheros' clubhouse that read: "If it's white, sniff it/If it's female or it moves, fuck it/If it narks-kill it". One member who joined the Comancheros in 1974 who idolised Ross was Anthony "Snodgrass" Spencer who saw him as a surrogate father who provided him with the love he never received from the father he had never known. Peter Edwards, the crime correspondent of The Toronto Star, described Spencer as very much a surrogate son to Ross.

Ross had an intensely authoritarian leadership style shaped by his military background and he gave himself the grandiose title of the "Supreme Commander". He was described as leading with "an iron fist". His favorite magazine was Soldier of Fortune, an American magazine catering to mercenaries and more commonly men who fantasise about being mercenaries. Like many other outlaw bikers, Ross's politics tended towards the extreme right and he had a gigantic Nazi swastika flag prominently hanging on the wall of the Parramatta clubhouse. Ross had the new members of the Comancheros swear allegiance to not only the Comanchero club, but also to himself as the "Supreme Commander". Ross led his men on weekly para-military drills intended to prepare them for brawls against rival bikers. The Comancheros were considered to be the most violent of Australia's many outlaw biker clubs in the 1970s and 1980s as Ross was constantly engaged in biker wars. The Canadian journalists Julian Sher and William Marsden wrote that Ross was well known for planning his attacks "with military precision". Sher and Marsden described Ross as a man with "disturbing visions of running his own private army". Besides for the endless drilling, Ross formed his own elite force of especially tough fighters, which he called the Strike Force. Many of the younger Comancheros who joined the biker gang in the late 1970s-early 1980s disliked Ross as one former member told the media: "If I wanted to march around in the fuckin' backyard, I would had joined the fuckin' army".

In 1980, Ross's first marriage ended in a divorce. That same year, the Comanchero had 20 members, but 7 suddenly resigned with Ross's former wife Sandra moving in with one of the members who had resigned, leaving the club with 13 members. Over the next three years, Ross expanded the Comanchero to 45 members, many of whom did not share the reverence that the members who joined the 1960s or 1970s did. In the early 1980s, Ross founded a fencing contracting business and was successful enough to be able to afford to buy a house in a middle class district in the West Pennant Hills. Ross started to date a single mother, Vanessa Eaves, whom he met in a bar. Ross described Eaves as the ideal "biker girl" who had a "a bit of fire" in her, but was ultimately submissive and docile towards her boyfriend. In the outlaw biker subculture, the girlfriends and wives of the bikers are considered to be "property" as the "biker girls" are treated as sex slaves who can be sold or bought. Simpson and Harvey wrote: "Comanchero men owned their women. Vanessa accepted this". Relations between Ross and Spencer went into decline when Spencer was not invited to Ross's second wedding in 1983. Ross's bride, Vanessa Eaves, had vetoed having "Snoddy" Spencer at the wedding under the grounds that: "Snoddy is always stoned and you know how stupid he gets. I'm not going to have him ruin my wedding".

In June 1983, the Comancheros became involved in a dispute with the Loners Motorcycle club. Ross led a raid on the Loners' clubhouse that ended with the three Loners present at the time of the raid being beaten bloody. Ross then suggested a meeting to discuss a truce, which proved to be a ruse. When the Loners arrived in the back alley for the meeting, they were surrounded and beaten up by a superior forces of Comancheros armed with baseball bats who took away their "colours". Ross forced the Loners to become a "feeder club" (i.e. a puppet club) for the Comancheros, which he named the Bandileros. There was continuing tension between the former Loners versus the original Comancheros. In addition, many Comancheros disliked Ross's leadership style, which was considered to be too authoritarian. The British journalist Annie Brown described Ross as "manipulative, violent and domineering". Colin "Caesar" Campbell, one of the anti-Ross Comancheros alleges that he and his brothers discovered that Ross was having an affair with another member's wife, which was a violation of the Comanchero rules. Ross had already come into conflict with "Caesar" Campbell who along with his brothers Philip "Bull" Campbell, Gregory "Shadow" Campbell, John "Whack" Campbell and Geoff "Snake" Campbell formed the core of the anti-Ross faction in the Comanchero. In July 1983, Ross had a shouting match with "Caesar" Campbell at a club meeting over the size of the clubhouse with Campbell demanding that the Comanchero move to a bigger clubhouse. Joined by his brothers along with Spencer, Campbell stormed out of the meeting.

The spokesman for the discontent in the ranks was Spencer. To avoid having to answer the charges that he violated his own rules against sleeping with the wife of another Comanchero, Ross split the Comancheros into two chapters; the ones unhappy with his leadership, led by Spencer, were assigned to a new chapter in Birchgrove. The Birchgrove chapter at 105 Louisa Road with Spencer as the chapter president opened in August 1983. Shortly afterwards, Ross was involved in an incident when he attempted to enter a pub in Kings Cross while being visibly drunk. Ross was refused admittance by the pub's Maori bouncers and was beaten up when he attempted to force his way in. Ross called upon all Comancheros to join him in beating up the bouncers in revenge, and was furious when Spencer declared that the Birchgrove chapter would not be involved. Spencer's decision to declare his neutrality was in turn sparked by his resentment at being excluded from Ross's wedding, which he took as a personal insult.