Mr Mason died March 4, 2014. He is one of many who died in 2014 that have not been registered yet. Currently there are 755 people whose death in 2014 is waiting for inclusion in Wikidata.
All these people are notable; they have a Wikipedia article. Mr Mason is notable because he published significantly on the subject of stress. His contribution to the understanding of stress was that the psychological and emotional state of the subjects under study required more careful attention.
You can relieve my stress by registering the deaths of these people. You can find them here.
PS as far as I am aware we do not register what people were relevant for, on what subject(s) they published.