Matthias was the PhD advisor of Matthew Flatt and Shriram Krishnamurthi at the time where (what would eventually become) the Racket project started. Virtually all of the core contributors are either his PhD students over the years, or students of his former PhD students after they became professors. He's the project's steward, being the person primarily responsible for securing grant funding for the work that goes into Racket, and the project's "visionary" (as much as such a thing can really exist), being the one who has most explicitly philosophized the concept of "language-oriented programming" (though there are plenty of other researchers now interested in the subject, including independently from Matthias' lineage). It'd be difficult not to understate the importance he has had to the careers of his former students (both in terms of the research they've done and in terms of his support in doing the politics necessary to have a successful career in academia).