James S.A. Corey is the pen name used by collaborators [Daniel Abraham][1] and [Ty Franck][2].
The first and last name are taken from Abraham's and Franck's middle names, respectively, and S.A. are the initials of Abraham's daughter.
[1]: https://openlibrary.org/authors/OL1427729A
[2]: https://openlibrary.org/authors/OL7523472A