Guix is based on the Nix package manager, which was designed and implemented by Eelco Dolstra, with contributions from other people (see the nix/AUTHORS file in Guix.) Nix pioneered functional package management, and promoted unprecedented features, such as transactional package upgrades and rollbacks, per-user profiles, and referentially transparent build processes. Without this work, Guix would not exist.
The Nix-based software distributions, Nixpkgs and NixOS, have also been an inspiration for Guix.
GNU Guix itself is a collective work with contributions from a number of people. See the AUTHORS file in Guix for more information on these fine people. The THANKS file lists people who have helped by reporting bugs, taking care of the infrastructure, providing artwork and themes, making suggestions, and more—thank you!