Roark Rickaby is a 23 year old Jazz violinist working at the Lackadaisy speakeasy. He was born in St Louis to Sophie and Ransom Rickaby- his mother's sister being Jeannine McMurray. Sophie has since died, and he has a strained relationship with his father, who would appear to have wandered off.
It seems from what is shown of the past that Nina McMurray spent a fair amount of time taking care of young Rocky. Enough time, certainly, for Freckle to 'enjoy' Rocky involving him in such healthy pursuits as glueing a pancakes to the poor boy's head to attract bees in the name of science, shaving all his fur off for the sake of sight gags, and attaching clothes pegs to his face.
Rocky spent time travelling from job to job and place to place in the past as is shown in Lackadaisy Correspondence, which shows his letters to Freckle from a variety of locations. He has worked in the circus as an escapologist, which is mentioned in the letter and can be seen in Lackadaisy scrapbook. This is a skill that comes in handy when tied up by a bunch of pig farmers in order to make a pretty mess under the wheels of the Sunshine special!
Rocky is, to put it mildly, eccentric, prone to rash behaviour, occasional outbursts of verbose poetry, manic grins and general foolishness. He has a definite soft spot for Mitzi, which is presumably the reason he's out there risking his neck getting tied to the train tracks and beaten up to obtain cheap moonshine for her as a rumrunner. He has managed to shoot a hole in his own earlobe by accident.