Leonard was a former associate of Theo Galavan.
According to Edward Nygma, Leonard worked for Theo Galavan before being kidnapped by Nygma.
Leonard was abducted by Nygma for Oswald Cobblepot so that Cobblepot would kill Leonard, as Cobblepot hated Galavan because of his mother's death. However Cobblepot was still grieving for his mother and wasn't in the mood for violence, so retired to bed and Nygma pulled Leonard away and locked him in a cupboard. After managing to convince Cobblepot he was better off without his mother, his more sadistic and murderous side resurfaced. The pair celebrated and Cobblepot asked Nygma if he still had Leonard. The pair of them then retrieved Leonard from the cupboard, as Cobblepot claimed it wouldn't be a party without "entertainment".