Henry McCarty (September 17 or November 23, 1859 – July 14, 1881), alias William H. Bonney, better known as Billy the Kid, was an American outlaw and gunfighter of the Old West who was linked to nine murders, four for which he was solely responsible, and five in which he may have played a role alongside others. He is also noted for his involvement in New Mexico's Lincoln County War.

McCarty was orphaned at the age of 15. His first arrest was for stealing food at the age of 16 in 1875. Ten days later, he robbed a Chinese laundry and was arrested again but escaped shortly afterwards. He fled from New Mexico Territory into neighboring Arizona Territory, making himself both an outlaw and a federal fugitive. In 1877 he began to call himself "William H. Bonney".

After killing a blacksmith during an altercation in August 1877, Bonney became a wanted man in Arizona and returned to New Mexico, where he joined a group of cattle rustlers. He became well known in the region when he joined the Regulators and took part in the Lincoln County War of 1878. He and two other Regulators were later charged with killing three men, including Lincoln County Sheriff William J. Brady and one of his deputies.

Bonney's notoriety grew in December 1880 when the Las Vegas Gazette, in Las Vegas, New Mexico, and The Sun, in New York City, carried stories about his crimes. Sheriff Pat Garrett captured Bonney later that month. In April 1881, Bonney was tried for and convicted of Brady's murder, and was sentenced to hang in May of that year. He escaped from jail on April 28, killing two sheriff's deputies in the process, and evaded capture for more than two months. Garrett shot and killed Bonney, by then aged 21, in Fort Sumner on July 14, 1881. During his short career as an outlaw, Bonney was the subject of numerous U.S. newspaper articles, some as far away as New York.

During the decades following his death, stories spread that Bonney had survived, and a number of men claimed to be him. The legend of Billy the Kid endures in American culture, and he remains one of the most notorious figures from the era, whose life and likeness have been frequently dramatized in the Western genre. He has been a feature of more than 50 movies and several television series.

Henry McCarty was born to parents of Irish Catholic ancestry, Catherine (née Devine) and Patrick McCarty, in New York City. While his birth year has been confirmed as 1859, the exact date of his birth has been disputed as either September 17 or November 23 of that year. There is uncertainty among historians about the exact place and date of McCarty's birth. Census records indicate that his younger brother Joseph McCarty was born in 1863.

Following the death of her husband, Catherine McCarty and her sons moved to Indianapolis, Indiana, where she met William Henry Harrison Antrim. The McCarty family moved with Antrim to Wichita, Kansas in 1870. After moving again a few years later, Catherine married Antrim on March 1, 1873, at the First Presbyterian Church in Santa Fe, New Mexico Territory, and the McCarty boys served as witnesses. Shortly afterward, the family moved from Santa Fe to Silver City, New Mexico and Joseph adopted Antrim's surname. Shortly before McCarty's mother died of tuberculosis on September 16, 1874, William Antrim abandoned the McCarty boys, leaving them orphans.

McCarty was 14 years old when his mother died. Sarah Brown, the owner of a boarding house, gave him room and board in exchange for work. On September 16, 1875, McCarty was caught stealing food. Ten days later, McCarty and George Schaefer robbed a Chinese laundry, stealing clothing and two pistols. McCarty was charged with theft and was jailed. He escaped two days later and became a fugitive, as reported in the Silver City Herald the next day, the first story published about him. McCarty located his stepfather and stayed with him until Antrim threw him out; McCarty stole clothing and guns from him. It was the last time the two saw each other.