Matt Mackall is the programmer who created Mercurial, the distributed version-control system, starting in April 2005. The Mercurial project’s own contributor wiki records that the primary author “started developing Mercurial in April 2005,” had been involved in open source development since the early 1990s, and led the project until retiring from it in 2016. (The project wiki now lists this developer under the name Olivia Mackall; the original 2005 work was published under the name Matt Mackall.)
Mackall introduced Mercurial to the world himself, in a message titled “Mercurial v0.1 - a minimal scalable distributed SCM” posted to the Linux kernel mailing list on April 20, 2005. In that announcement he described the system’s goals: “to initially be as simple (and thereby hackable) as possible,” and “to be as scalable as possible” and “memory, disk, and bandwidth efficient.” He noted that the working prototype was “all in less than 600 lines of Python.”
The timing was deliberate. Earlier that month BitMover had announced it was withdrawing the free version of BitKeeper, the proprietary tool the Linux kernel had relied on, which left kernel developers without a distributed version-control system. Mackall’s Mercurial was one of two responses that appeared almost simultaneously; the other was Linus Torvalds’s git. Both began in April 2005.
Mackall went on to lead Mercurial’s development for more than a decade, presenting on its design at venues including the Linux Symposium. Where git won the widest adoption, Mercurial built a durable following at organizations that valued its clean, Python-based design.