I've met Thomas when he was PhD. student at Linz university. He is one of the most skilled people when it comes to knowledge of HotSpot VM. For example he implemented true Hotswap for JDK (which is still waiting for inclusion into JDK, as the JDK guys are gang of nuts doing stupid things and not the stuff important to attract developers). Visit http://ssw.jku.at/dcevm/
Oracle labs found Thomas so important, that they created a special subsidiary for him in Linz. Thomas still sits at the (almost) same office as I met him first time, but now working for Oracle on the Graal project.