The first badges (and their names) were most likely dreamt up in the early days of the site internally. I imagine a brain storming session was held or something of that nature.
After the initial badges, more were (and continue to be) added. The names and definitions were discussed here on Meta and the community weighed in with their (our) opinions... This is the purpose of badge-request. Combine that tag with the status-completed tag, and you'll be able to see all of the suggestions that were implemented.
