ssh-keygen - how to set an rsa key with a certain username

I just installed ubuntu and would like to set its rsa keys up with bitbucket/github. When I ssh-keygen the keys are generated as they should be ssh-rsa AA...yBEz3pLL georgemauer@ubuntu which is perfectly usable except the username part. In every rsa key I've generated previously, the username section read my email address: ssh-rsa AA...yBEz3pLL gmylastname@gmail.com No, it's not a major impediment but if I don't get this right it will drive me crazy. How, do I generate with rsa keys with an email username of my choice?