This name foremost comes from his preference to the color green, and secondly to distinguish him from the three other Hans’ in the apprenticeship. He later included it in his monogram, and it has also been suggested that it came from "grienhals", a German word for witch. Hans quickly picked up Dürer's influence and style, and they became good friends. In his later trip to the Netherlands in 1521 Dürer's diary shows that he took with him and sold prints by Baldung.
source: www.artisoo.com
