I found Hibernate while I was evaluating data access solutions for an upcoming Java project, back in early 2002 when Hibernate was virtually unknown. It was the only software that made it through my small evaluation testcase. I realized that other people would probably have the same problem and started contributing more and more to the project Gavin King founded.
Hibernate grew at a very impressive and sometimes overwhelming rate. We wrote the book Hibernate in Action, for users of Hibernate and also to nail down core Hibernate concepts in a formal way.
Two years later, many of these ideas have made it into the Java Persistence specification, part of the Java EE 5.0 and EJB 3.0 industry standards. The new book we wrote, Java Persistence with Hibernate, describes how Hibernate changed during that time, and what the latest version can do.