Each type of source control system represents authors in a different way. For example, a Git commit author has a display name and an email address, but a Subversion commit author just has a username. The GitHub Importer will make the author information valid, but the author might not be correct. For example, it will change the bare Subversion username hubot into something like hubot <hubot@12341234-abab-fefe-8787-fedcba987654>.

This endpoint and the Map a commit author endpoint allow you to provide correct Git author information.
Get commit authors