Current:
- Intel, created and holds most copyrights for IA-32
- AMD, created and holds copyrights for x86-64
Past:
-
VIA https://en.wikipedia.org/wiki/VIA_Technologies . Bought:
- Cyrix https://en.wikipedia.org/wiki/Cyrix from National Semiconductor
- Centaur https://en.wikipedia.org/wiki/Centaur_Technology
Intel and AMD are the major ones.
Cyrix was an implementor before being bought by National Semiconductor, and VIA continue to produce them after buying Cyrix from NS.
You need a license to implement x86, at least the parts which are newer than 20 years ago:
- http://arstechnica.com/civis/viewtopic.php?f=8&t=852658
- Cyrix got into trouble for not licensing it https://en.wikipedia.org/wiki/Cyrix#Legal_troubles
Intel and AMD have cross-licensing agreements:
- http://www.kitguru.net/components/cpu/anton-shilov/amd-clarifies-cross-license-with-intel-change-of-control-terminates-agreement-for-both/
- http://www.sec.gov/Archives/edgar/data/2488/000119312509236705/dex102.htm
- https://www.reddit.com/r/hardware/comments/3b0ytk/discussion_what_is_an_x86_license_and_why_do/
- http://www.anandtech.com/show/2873
- http://www.eetimes.com/document.asp?doc_id=1129690
- Interview with W. Jerry Sanders http://silicongenesis.stanford.edu/transcripts/sanders.htm
https://github.com/marmolejo/zet TODO legal?