They’re the company that created Cardano. They’re well-respected for their code quality and the use of formal methods and academic peer review to develop their software. They started out an enemy of most Haskell devs then won many over with their massive open source contributions to the Haskell developer experience. Their Nix based Haskell dev environment is THE best way to use Haskell with Nix.
They used to be called IOHK or Input Output Hong Kong which is still reflected on their GitHub.