He habitually wore a fringed buckskin jacket, a wide brimmed hat, and was “fully laden with a twin-gun harness that added a lethal touch.” (The Tombstone Epitaph) He was 5-feet, 7-inches tall, and wore boots with 2-inch heels to stand a little taller.
He took up with the buxom but married Mary Killeen in June of 1880, killed her husband when the man came after him with a Colt in his hand, and married the widow in July. Killed Billy Claiborne outside the Oriental Saloon in 1882 when the little gunslinger wannabe picked a fight with him, and remains a prime suspect in the death of John Ringo, but what did him in was the death of Molly Williams. Molly was a whore who worked the cribs at the Birdcage Theater, and moved in with Frank when he split up with the widow Killeen. Drunk and quarreling one night in 1887, Molly pulled a little pocket pistol, but Frank shot first, and she died. The upshot of that: 25 years in Yuma.
The early release is generally attributed to the fact that during several outbreaks of disease at the prison, he worked hard and at great risk to himself caring for fellow inmates and staff. (So maybe he had gone to medical school...) The physician in charge wrote that Leslie "was a most humane and self-sacrificing attendant."
So he gets out in 1897 and other adventures ensue... Cuba during the Spanish-American War, some time working a coal field survey in Mexico, prospecting for gold in Alaska, another marriage or two... In 1904 he was managing a grocery store in San Francisco, and by 1913 running a pool hall in Oakland. One source says he committed suicide in 1925, another that he died drunk and penniless in 1930. Either way, a bad end in his eighties.
Postscript: Josephine Earp wrote that she and Wyatt ran into Frank Leslie in Oakland one day in the 1920s. He was an old man, in "pitiable" condition, she said, and recalled that Wyatt slipped him a little cash before they parted.
She said they never saw him again.