I've watched this (excellent) panel discussion titled 'Our Future in Space'. Bill Nye says at 22:48 that SpaceX got their engine design from work done by NASA, which they developed into a working production model. What design was that and what documents did they use? And can I get those documents?
The Merlin uses a pintle injector, a design first used in the Lunar Module Descent Engine, developed from original work at Caltech and JPL. Its design was publicized as U.S. Patent 3,699,772. It's a design (PDF) that was used a lot by patentor TRW.
A TRW employee, Tom Mueller, got bored with his day job and started working in his spare time on engines for model rockets. Around 2001, he was working on an engine capable of 13,000 lb of thrust (the biggest model rocket engine in the world). Elon Musk hired him and put him to work building "something bigger". Mueller became one of the founding employees of SpaceX and was Vice President of Propulsion Development as of 2013.
Musk sought Mueller out in 2001 when Musk decided to build his own rockets instead of buying some from the Russians. Musk caught wind of a rocket engine Mueller built in his garage and “apparently had a religious experience” once he saw it. If you didn’t know, Elon Musk used $100 million of his Paypal money to start SpaceX. That money was used to build the Merlin engine Mueller had designed.