Onni Bovellan was born in Kiuruvesi, Finland on 27 December 1917 to parents Joona Bovellan and Olga Miina Kärkkäinen. He was a frail child and was not originally expected to live long. However, he survived and became healthy. After finishing school, Bovellan went to work in a sawmill. In the Winter War, Bovellan fought in Colonel Hjalmar Siilasvuo's troops. He led many successful patrols to Soviet territory and was awarded the Iron Cross.