Until recently, the Zassenhaus Group Theory Conference merged with the Ohio State-Denison Mathematics Conference in even-numbered years, with the group theorists meeting in the odd-numbered years at various locations around the country. The even-numbered year conferences held in Ohio originally included group theory, ring theory, and combinatorics (areas in which Hans Zassenhaus was active). 
The Ohio State University Department of Mathematics maintains a website with more information about the life and work of Hans Zassenhaus, as does MacTutor History of Mathematics Archive.