The Tcl/Tk core is managed by the Tcl Core Team and the Core Maintainers.
The Tcl Core Team act as a technical oversight board for new features for the core. They are trying to make sure that as many people as possible are happy with each new feature that is added and that the overall effect is coherent.
The Core Maintainers are the people who do the actual code-editing work and have the right to modify the core. You can become a core maintainer if you want! Just tell the TCT your SourceForge user-id and say what bit of the core you want to maintain.