Marek has been working on the open-source Mesa/Gallium3D driver code for years and has been covered dozens of times on Phoronix with the various improvements, new features, and better performance offered by his work. He's made countless contributions to Mesa and is one of the top contributors to Mesa. His contributions are very well known within the Phoronix Forums, where he is also an active member.
Marek has been working on the Radeon Gallium3D code the most and he's been doing this work not as an employee of AMD or some stakeholder, but rather just an independent contributor while studying at university. AMD offered him a job previously, but he wanted to finish his studies. He's basically been scratching his own itch with regard to working on the open-source AMD Linux graphics drivers.
For those that haven't yet noticed yet from the mailing lists or today's several Radeon Gallium3D improvements, he's now committing from an email address at AMD.com rather than Gmail. I asked Marek today on IRC about the situation and he confirms that he is now employed by Advanced Micro Devices.
Congratulations to Marek Olšák on joining the open-source AMD Linux graphics team! AMD in the past as well has recruited their open-source developers from active open-source Radeon developers. Hopefully Marek's pace of activity will now only rise with university studies out of the way and already today were many new commits from his new AMD email address.