It was written by the AWS Well-Architected team, and is based on curating best practices from Solutions Architects working with customers and engineering teams. Its one of Six main papers, with the main framework, and then one per pillar https://aws.amazon.com/architecture/well-architected/

There is also a free tool available to review architectures. https://aws.amazon.com/well-architected-tool/

The aim is to help customers learn best practices for building and operating in the cloud. (I work in the AWS Well-Architected team)