Mase is a person, he used to frequent the UK on a regular basis and people would book a while in advance to get him to tune their cars. Believe he‘s based in the USA?
As jimmer said mase is one guy from the US and he use to come round the UK for tuning, i got to meet him once when my brother had his k20 eg9 tuned by him. He was One of the best tuners at the time bit sure if he is still doing it tho