Just looking at the IMDB cast list of the Mentalist;

Simon Baker... Patrick Jane (122 episodes, 2008-2013)
Robin Tunney... Teresa Lisbon (122 episodes, 2008-2013)
Tim Kang... Kimball Cho (122 episodes, 2008-2013)
Owain Yeoman... Wayne Rigsby (122 episodes, 2008-2013)
Amanda Righetti... Grace Van Pelt (122 episodes, 2008-2013)
Aunjanue Ellis... Madeleine Hightower / ... (17 episodes, 2010-2013)
Michael Gaston... Gale Bertram (17 episodes, 2010-2013)
Gregory Itzin... Virgil Minelli (15 episodes, 2008-2012)
John Troy Donovan... CBI Ron (13 episodes, 2010-2013)

CBI Ron is the guy who shows up in the series in number 4 apart from our team. I don't remember Ron doing anything important just stuff like get this, send that, phone this person like that. I mean is this guy know someone from casting crew or is he RJ ?
(Seriously this guy must be a some important chacter)