Minor clarification of the clarification: the author of Cap'n'proto was the original creator of Proto2, which was a ground-up (but binary compatible) rewrite of Proto1. The original authors of Proto1 were Jeff Dean & Sanjay Ghemawat. The current version of protobufs is Proto3, which AIUI is maintained by a team at Google (it was released after I left), and is an evolution of the Proto2 codebase with many new features.
