From the Traveller RPG Wiki on wikia.com:
Gareth Hanrahan is a gaming author and freelance writer. He has written for White Wolf, Alderac Entertainment, Green Ronin, and most recently Mongoose Publishing as the author of Mongoose Traveller Main Rulebook. Gareth lives and works in Ireland.
From Serpent King Games website:
Gareth is a freelance writer and game designer; he’s been writing full-time for roleplaying games ever since he escaped from his previous life as a computer programmer. Most of his work has been for Mongoose Publishing; he was a staff writer there for seven years, writing millions of words for d20. Babylon 5, Conan and other lines. He was the designer of the newest edition of the venerable Traveller roleplaying game, as well as the 25th anniversary edition of Paranoia.
Outside of Mongoose, he’s written for Hogshead Publishing, Green Ronin, Paizo, Pelgrane Press, AEG, FFG, WW, WotC and many other corporate acronyms. He’s a fixture of the Irish gaming scene, whatever that means.
His personal tastes in gaming tend towards things flavoured with Cthulhu, intricate adventures, and collaborative campaign design.