The maintainer of the JavaParser project is Danny van Bruggen a.k.a. Matozoid.
There are over 100 people who contributed to JavaParser. Among them a few have more commits than others: Federico Tomassetti, Nicholas Smith, Cruz Maximilien, and Sebastian Kirsch.
Projects using it
There are more that 50 libraries available through Maven that depend on JavaParser, over 1300 maven projects on GitHub, and a number of commercial projects.
The parser is based on work by Sreenivasa Viswanadha and Júlio Vilmar Gesser. The original parser created in 2008 was for Java 1.5 and hosted at Google Code.
Danny van Bruggen picked it up and put it on GitHub. He started accepting patches. Over time a community grew around it. In 2015 Federico Tomassetti started working on the JavaSymbolSolver which in 2016 was included in the JavaParser set of tools. He also added the lexical preserving parser.