Little is known about Kieran's background prior to 1899. His father was an Irishman with a dream of farming West in California, but would inevitably die of cholera with Kieran's mother suffering the same fate. This left a young Kieran orphaned. At some point, Kieran became a member of the O'Driscoll Boys, a rival of the Van der Linde gang. He also mentions that he has a good knowledge of horses, as he worked as a stable boy for the O'Driscolls.