First Appearance: Gunsmoke Western #54 (September 1959).
Appearances: Western Team-Up #1, Mighty Marvel Western #23, Wyatt Earp #25, Gunsmoke Western #54-55, Kid Colt Outlaw #87, 176.
Years Active: 1870s.
I have not yet succeeded in reading an origin for the Gunsmoke Kid, if one such exists. The Kid has a bad reputation (as you can tell from the panel) but is a good man, interested in peace rather than fighting. The Gunsmoke Kid (I've not even been able to find his real name) is good with his fists and quick with his guns ("the fastest gun west of the Mississippi"), and is, like many another Marvel cowboy character, a wandering shootist, not tied to one place. He's actually rather good-natured, and although he keeps a Derringer up his sleeve his stories usually involve him wandering through a town, trying very hard to avoid a fight, being drawn reluctantly into a conflict (usually between other people; his own reputation is enough to scare most people and would-be gunslingers off), settling it (as often with words as with his fists or guns), and then leaving town. Even when he's riled he almost always threatens others without actually drawing his guns.
I have not been able to find anything of his origin, but one story did contain a glimpse of backstory: after helping to catch some cattle rustlers he rides off, looking at a picture and thinking, "I said I'd make you proud of me, Ma! At least I've made a start!"