Hermann was born in 1938 in Bévercé (now a part of Malmedy) in Liège Province. After studying to become a furniture maker and working as interior architect, Hermann made his debut as comic book artist in 1964 in the Franco-Belgian comics magazine Spirou with a four page story. Greg noticed his talent and offered him to work for his studio. In 1966, he began illustrating the Bernard Prince series written by Greg, published in Tintin magazine. In 1969, also in collaboration with Greg, he began the western series Comanche. This appeared at the same time as other western series such as Blueberry.