He wrote the books to Broadway Musicals. Thomas won Tony Awards writing the books to probably the three biggest musicals of my life time. If they weren't the biggest they were near the top. Annie, Hairspray and The Producers.
Above a clip from Hairspray below a clip from The Producers...
I was able to review a production of Hairspray at The Signature Theatre in Alexandria, Virginia outside of Washington when I wrote for the Maryland Theatre Guide. You can revisit that review from 2011 here.
He also wrote the books for the musicals Rocky and Elf. He also wrote the book for one of my favorite movies when I was a kid Spaceballs. He was a successful writer who lived a long life. He will be missed.