David Mayo is a former Scientologist and Sea Org member. At one point he was the person in charge of the accuracy of the church scripture. However, in 1983, he was declared a Suppressive Person and permanently expelled from the Church for creating technical havoc by falsifying reports, passing along materials created by him as scripture of L. Ron Hubbard and - by altering Scientology procedure - potentially threatening the viability and mental health of thousands of Scientologists by his actions. He ultimately joined up with others in altering stolen OT information and attempting to deliver it to the public. This group failed.
I have no idea where he is today, but he seems to be staying away from the Church's affairs.
Robin Scott Court Papers
David Mayo Suppressive Person Declare