This guy, both an official Ubuntu developer and a core CPython developer, is a great example of a FLOSS collaborator. He is always polite on mailing list discussions, kindly and patiently helps foster collaboration between Debian and Ubuntu (there's been some conflicts between the two camps). This is on top of his superb technical efforts demonstrated by his highly-detailed guides on various things, like upgrading various Python projects to run on Python 3 (example 1, example 2, example 3).