Nicco holds this together. He maintains the most packages amongst the team, reviews code across the whole ecosystem, brought most of this team together, and is the primary contact for NLnet. The coordinated effort you see here is largely his doing.
The original. Tobias started building CalDAV tooling in 2013 because he needed it, not because it was a project. That work became calendar-cli, then python-caldav, then plann. Over a decade later he still maintains all three and knows where every server quirk is buried.
Abe runs MergeCal.org and MyHebrewDates.com on these packages, which means he hits the bugs that only show up at scale. He maintains python-mergecal and django-icalendar, and is also a maintainer of dj-stripe.