Jackie was found as an infant by Albert Marr (some accounts refer to him as Andrew) on the family smallholding in Villieria, now a suburb of Pretoria on the southern side of the Magaliesberg. He had probably been orphaned by bounty hunters who were paid by the Transvaal government to shoot baboons raiding crops in the Moot Valley. Albert took the young baboon home and he was raised as a member of the family much like a human child. Jackie and Albert became inseparable.
In 1914 South Africa joined the Allies in the First World War and the two-year-old Union Defence Force called for volunteers to serve, first in German South West Africa and then in East Africa. In 1915 the 3rd South African Infantry Regiment was formed to join the South African Overseas Expeditionary Force in North Africa and Europe. Albert Marr volunteered to join the regiment but requested not to be separated from his beloved baboon. Lt. Colonel Edward Francis Thackeray, Officer Commanding the 3rd South African Infantry, agreed to allow Jackie to join as the regimental mascot.