Question: Why did Ken Shamrock change his last name?
Evidence: Kenneth Wayne Shamrock (né Kilpatrick; born February 11, 1964) is an American bare-knuckle boxing promoter and semi-retired professional wrestler, mixed martial artist, and kickboxer. He is best known for his time in Ultimate Fighting Championship (UFC) and other combat sports. A member of the UFC Hall of Fame, Shamrock is widely regarded as an icon and pioneer of the sport. He has headlined over 15 main events and co-main events in the UFC and Pride FC and set numerous MMA pay-per-view records. In the early part of his UFC career, Shamrock was named "The World's Most Dangerous Man" by ABC News in a special called "The World's Most Dangerous Things". The moniker has stuck as his nickname.

Shamrock became known early on in the UFC for his rivalry with Royce Gracie. After fighting to a draw in the inaugural UFC "Superfight", he became the first UFC Superfight Champion when he defeated Dan Severn at UFC 6; the title was eventually replaced by the UFC Heavyweight Championship when weight categories were introduced to the UFC. He was also the first foreign MMA champion in Japan, winning the title of King of Pancrase Openweight title. During his reign as the UFC Superfight Champion, he was widely considered the #1 mixed martial artist in the world, and in 2008, Shamrock was ranked by Inside MMA as one of the top 10 greatest mixed martial arts fighters of all time. He is the founder of the Lion's Den mixed martial arts training camp, and is the older brother of fellow fighter Frank Shamrock.

In addition to his mixed martial arts career, Shamrock enjoyed considerable success in professional wrestling, particularly during his tenure with the World Wrestling Federation (WWF, now WWE). There, he is a one-time Intercontinental Champion, a one-time World Tag Team Champion and the 1998 King of the Ring. Shamrock also wrestled for Total Nonstop Action Wrestling (TNA, now Impact Wrestling), where he is a one-time NWA World Heavyweight Champion – the first world champion under the TNA banner – and a 2020 inductee in the Impact Hall of Fame. He headlined multiple pay-per-view events in both promotions, including 1997's D-Generation X: In Your House, where he challenged for the WWF Championship. Additionally, Shamrock was also one of the first wrestlers to use the shoot style of wrestling in America, being credited by WWE with popularizing the legitimate ankle lock submission hold.

A "military brat," Kilpatrick was born at Robins Air Force Base, in Warner Robins, Georgia, where he lived for his first four years. His father Richard Kilpatrick was a United States Air Force enlistee, and his mother Diane Kilpatrick was a waitress and dancer who had her first son when she was 15. Shamrock had three brothers and came from a broken family in a predominantly black neighborhood of Atlanta, Georgia.

He was often left to fend for himself, and, without his parents' supervision or guidance, got into many fights. His father abandoned his family when Shamrock was five. His mother married an Army aviator named Bob Nance, and the newly formed family moved to Napa, California, Nance's hometown. Shamrock and his brothers were outsiders in this community, coming from a poor background and speaking in a Southern accent. They continued to cause trouble and get into fights and began using drugs. Nance, who fought in the Vietnam War, joined the local fire department and also worked in roofing and upholstery. Shamrock became involved in and excelled at sports at a young age, playing in Little League baseball and Pop Warner football. Nance remembers a veteran coach telling him that he had never seen a player with as much heart and tenacity as the young Shamrock. Shamrock was not as involved with drugs as his brothers, such as his brother Richie, who enjoyed smoking marijuana and eventually using heroin intravenously, but who also played football.

At age 10, Shamrock ran away from home for the first time, and was stabbed by another child on the run, ending up in the hospital. When he was 13, his stepfather kicked him out of their home, and each of the brothers went their own ways. Shamrock lived in cars before being placed in a foster home. He went through seven group homes and served time in a juvenile hall. He moved between several more group homes before being placed in Bob Shamrock's Boys' Home at age 14 in Susanville, California where he turned his life around. Bob Shamrock legally adopted Ken as his son, and Ken changed his last name from Kilpatrick to Shamrock in Bob's honor.

At Lassen High School, Shamrock (known there as Kenny Nance) excelled in football and wrestling. As a senior, he qualified for the state championships in wrestling, but broke his neck in practice days before the competition and underwent neck surgery. He received no scholarship offers from any big colleges, and doctors told him his sports career was likely over. Against doctors' orders, he joined the Shasta College football team, where he was voted team captain in his final season. The San Diego Chargers of the National Football League later offered him a tryout, but he declined in order to pursue a career in professional wrestling, where he debuted in 1989 in the South Atlantic Pro Wrestling promotion.
Answer: Ken Shamrock changed his last name from Kilpatrick to Shamrock in honor of his adoptive father, Bob Shamrock.  Bob Shamrock legally adopted Ken after Ken was placed in Bob Shamrock's Boys' Home, following a period of homelessness after being kicked out of his stepfather's home, several foster homes, group homes, and a stint in juvenile home.