They were one of the first users of Mesos, but they didn't create it.
> Mesos began as a research project in the UC Berkeley RAD Lab by then PhD students Benjamin Hindman, Andy Konwinski, and Matei Zaharia, as well as professor Ion Stoica.
> The social networking site Twitter began using Mesos and Apache Aurora in 2010, after Hindman gave a presentation to a group of Twitter engineers.
Then Mesosphere (a company) wanted to bring it to the enterprise market but at the time was competing with Kubernetes... and we all know who won.