[logn]

Gorhill wrote uBlock. After the project took on a life of its own, Gorhill handed the primary repo over to the contributors so he could develop from a fork of it. The primary repo then introduced requests for donations, changed attribution/authorship, and ended some features. As a result of the feature set difference, Gorhill renamed his fork to "uBlock Origin" so the features he wanted would be available in the addons sites without conflicting with "uBlock". At this point given their divergence, both projects are fully maintained and developed in parallel, with relevant revisions merged to each other where possible.

That's the neutral summary at least.

(edited slightly for clarity)