Pgpool-II started its life as a personal project by Tatsuo Ishii. In the project it was just a simple connection pooling software. So the name Pgpool came from the fact. The first version was in public in 2003.
In 2004, Pgpool 1.0 was released with the native replication feature (SQL statement based replication). In the same year 2.0 was released with load balancing, and support for version 3 frontend/backend protocol. In 2005, automated fail over and master slave mode support were added.
In 2006, Pgpool became Pgpool-II. The first release 1.0 eliminated many of restrictions in Pgpool, for example the number of PostgreSQL servers was up to 2 in Pgpool. Also many new features such as parallel query mode and PCP commands (PCP stands for "Pgpool Control Protocol") were added. Probably the most important change made between Pgpool and Pgpool-II was that the project was changed from a personal project to a group project owned by the Pgpool Developement Group.