As in Deputy Marshal Earp of O.K. Corral fame? Well, to the best of my knowledge he was a fugitive himself in 74', working a prostitution ring with his brother out of Peoria, later in his career to use the alibi of having been hunting buffalo between 71' and 75', and hadn't yet been deputized as a US Marshal, though it would certainly explain his happening to have connections in and out of the Confederacy to free Canada. I like Bill better for the role myself, because he was not only a legend at the time unlike Wyatt Earp who became famous after the O.K. Corral, but someone few truly knew. The guy was an actor more than anything else at the end, who dressed dandily when socializing with the aristocracy who so loved the legend, dressed in the skins of a mountain man when putting on shows with Buffalo Bill, which is what he was doing in 74, mostly to get enough money together to drown his problems in a bottle and play poker, who held a deep appreciation for the culture of the Cheyenne whilst harboring an illogical grudge bordering on jingoism towards them, fought as an enlisted scout alongside the 10th Cavalry (an otherwise segregated black regiment) despite having better offers at the time, hated those who sought to hold authority over him, and always rooted for the underdog. Doesn't hurt that his father was an abolitionist who worked the underground railroad, and James himself fought originally for the Kansas Free State Army, General Lane's famed Jayhawkers.
Wild Bill had his faults, grievous ones, perhaps. He would get drunk, gamble, and indulge in the general licentiousness characteristic of the border in the early days, yet even when full of the vile libel of the name of whiskey which was dealt over the bars at exorbitant prices, he was gentle as a child, unless aroused to anger by intended insults. He was loyal in his friendship, generous to a fault, and invariably espoused the cause of the weaker against the stronger one in a quarrel. ~ Captain Jack Crawford
EDIT:
I am writing the modified background of James Hickok now, and will be operating under this historical fiction timeline. If you have any questions, concerns or simply dislike anything I've listed here let me know, and I'll immediately edit accordingly:
---: May 27, 1837; James Butler Hickok, born in Troy Grove, formerly Homer, Illinois, US, to William and Polly (Butler) Hickok.
---: 1849; James has his first experience under fire whilst transporting escaped slaves by wagon across the Mississippi from St. Louis back home to Madison County.
---: 1851; William Hickok is killed just West of the Mississippi, in Missouri, by St. Louis lawmen while, "stealing," Southern plantation owners property, slaves.
---: 1854: Takes a job in Utica, Illinois, as a wagon driver on the Illinois and Michigan Canal.
---: 1855; After a confrontation over the treatment of his horse team, kills his employer, Charles Hudson, by drowning him in a river, and flees the state to Leavenworth, Kansas. Fearing legal retribution for the murder begins going by the name William Hickok.
---: 1856; Joins General Lane's Free State Army, the Jayhawkers, as an irregular militiaman.
---: 1858; General Lane begins grooming James for leadership in his, "New," Kansas.
---: 1861; Kansas is admitted to the Union as a Free State. The McCanles Shootout marks the first time James kills a man in a gunfight. The Civil War begins, and at Lane's insistence, "Wild Bill," Hickok signs on as a civilian Wagon Master for the Union Army out of Sedalia.
---: September, 1862; Hickok is discharged for reasons undisclosed, and disappears for a year until resurfacing in late 1863.
---: 1863; James takes up employment as a deputy of the Provost Marshall in union held Springfield, Missouri.
---: 1864; The first recorded instance of what would become a Western staple for the next decade takes place, as Wild Bill Hickok kills Dave Tutt in a quickdraw standoff. Surrenders the town of Springfield to the encroaching Confederate forces in light of the Union withdrawal.
--- 1867; Having previously been deputized as a US Marshall, transfers to Hays City, and acts as city marshal, several of his most gunfights occurring at this time. Is contacted by Rail Splitter agents, and begins secreting escaped slaves North through Kansas to what remains of free Canada.
--- 1871; James serves as city marshal of Abilene, Kansas.
--- 1873; Wild Bill Hickok joins Buffalo Bill’s show Scouts of the Plains.
--- 1874; James leaves the show after his final stage performance in Richmond, Virginia, his health failing, ready for one last job. The assassination of President Jackson.