Steffen was born into a family of eight children in Chicago. He studied drawing, art history, and photography in the late 1940s. However, his Catholic faith prevented him from embracing the ideas presented in a philosophy class, and in a fit of anger, the young student burned his work, threatened suicide, and ultimately fell into a deep depression that forced him to leave the institution barely a year after enrollment.

He was hospitalized and underwent treatment and electroconvulsive therapy for schizophrenia. After leaving the hospital, unable to find employment, Steffen returned to his family home to live with his sister, Rita, who asked him to regularly destroy his piles of drawings due to the risk of fire.

Steffen primarily drew with colored pencils on brown paper bags, producing one to three drawings a day. All of his work dating from before 1989 has been destroyed.

His fantastical universe is populated by metamorphic creatures subjected to hybrid mutations between human, animal and plant.