Working as a cowboy and bounty hunter, Mountain Tim is announced as a leading competitor in the Steel Ball Run. During the first stages of the race, Tim becomes one of Johnny and Gyro's allies. He is also a Stand User and shifts through his lasso thanks to his stand, Oh! Lonesome Me.

Mountain Tim is a man of average to above-average height and average build. Handsome and light-haired, he later acquires a scar crossing his face.
He wears a stereotypical range of cowboy attire; his hat has a zebra print, while the clothing on his upper torso, his belt gun holster, and his scarf have a leopard print. He wears a sheriff's badge in the shape of a five-pointed star on his left side.

Oh! Lonesome Me enables Mountain Tim to separate segments of his or others' bodies and freely slide them along a rope. It also grants him superhuman control over the rope, freely and precisely manipulating it to grab small objects from afar for instance.
This ability to separate himself into little pieces as far as the rope goes grants Mountain Tim greater agility and flexibility. Launching himself along it, Tim may shoot enemies from odd angles; and through the process of splitting and joining himself and others back together, he may travel and escape through small spaces.

Possessing a mysterious mastery of equestrianism, horses tend to bow their heads in his presence.

(Source: JoJo's Bizarre Encyclopedia)

Riders from around the world gather in the Wild West for the race of the century! Johnny Joestar, a former jockey paralyzed from the waist down, comes to spectate, and momentarily regains the ability to walk while watching a duel fought by Gyro Zeppeli. Desperate to learn more about this power, Johnny joins the race alongside Gyro and embarks on the most epic and bizarre race to ever cross the American frontier! 
(Source: VIZ Media)

The beginning of the seventh story arc in the long-running JoJo's Bizarre Adventure series. 

It’s 1890, in America, the Steel Ball Run — the first horse racing championship across the North American continent — was about to begin. Johnny Joestar, once being hailed as a genius jockey, is now paralysed and lost in despair. He finds hope in the mysterious phenomena caused by Gyro Zeppeli, an outlaw aiming to win the race, and determines to participate in the 4,000 miles of grueling adventure. 

(Source: STEEL BALL RUN: JoJo no Kimyou na Bouken Site)