Leo arrived at the Sanctuary in 2002. Born in the Goiânia zoo, Brazil, he was abandoned by his mother. As a result, he was raised as a human in the home of a zoo employee. When he grew up and became uncontrollable, as is typical, he was returned to the zoo and mistakenly placed with his parents, who no longer recognized him. He was attacked by his father and had to be immediately removed from the enclosure. He was then placed in a small temporary enclosure and isolated, where he began to fall ill and develop pathological behavior.

His case was discovered by an NGO, and the solution was to take him to the Brasília zoo, where he would have better chances of integration. However, after some time, he came into conflict with Junior (a chimpanzee who would also go to the Sanctuary, in 2005), and the solution found was to transfer him permanently to the Sanctuary.

Leo spent the last years of his life at the Sanctuary with Monica. He passed away in 2007.