Clarence Ellis was an American computer scientist, and Emeritus Professor of Computer Science and Cognitive Science at the University of Colorado at Boulder. While at the CU-Boulder, he was the director of the Collaboration Technology Research Group and a member of the Institute of Cognitive Science. Ellis was the first African-American to earn a Ph.D. in Computer Science (1969), and the first African-American to be elected a Fellow of the ACM (1997). Ellis was a pioneer in Computer Supported Cooperative Work (CSCW) and Groupware. He and his team at Xerox PARC created OfficeTalk, one of the first groupware systems. Ellis also pioneered Operational Transformation, which is a set of techniques that enables real-time collaborative editing of documents.