With 107 commits under his belt, the #78 Rails committer is Jason Noble.
Jason was active from 2011 to 2012. The majority of his commits were documentation commits. He racked up an incredible 84 changes in just the Getting Started guide alone — and that covers both its early Textile format and the more modern Markdown format that the guides now use. My guess is that he wrote the whole thing, or at least the whole thing as it existed at the time. Jason also fixed ActiveRecord bugs, namespaced its fixtures, and added deprecation warnings.
Big thanks for all your hard work!