According to the Apache Tomcat release page Tomcat 3.0 was the initial release of Tomcat:
Apache Tomcat 3.0.x. Initial Apache Tomcat release.
What happened to Tomcat version 1.x and 2.x?
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There has never been a Tomcat version 1.x or 2.x. Tomcat came to life as a merger between Apache JServ (which implemented the Servlet Spec 2.0 in its last version) and Sun's reference implementation of the Servlet Spec 2.1. The first release of Apache Tomcat was then 3.0 - see also http://tomcat.apache.org/heritage.html.