So you don't have to do the "research" yourself:
https://freebsdfoundation.org/our-donors/donors/
https://freebsdfoundation.org/our-donors/donors/?donationYea...
BTW: Those are just the monetary donations towards the foundation, additionally you have developers that are directly paid to work on the FreeBSD project (search for "Sponsored by"):
https://www.freebsd.org/releases/14.1R/relnotes/
https://www.freebsd.org/releases/13.3R/relnotes/