Lieutenant Ana Ruiz is Jack and Dan's boss and she sees to it that they keep themselves and the police department out of trouble by investigating seemingly minor crimes, the Code 58s.
Initially Lt Ruiz is portrayed as a strict, by the book cop who is not too fond of Jack and Dan. As the first season progresses Ruiz, or Lt as she is called, is found to be more compassionate and understanding than expected. Other things are revealed too. Along with Frank Savage she is a former partner of Dan's. She and Dan had a brief romance. On his car. They made a naughty video. Despite her tough exterior Ruiz genuinely does care for Dan, as a friend. She has a very high tolernce for Dan's behaviour, though she isn't above suspending him when he crosses the line. When Internal Afairs comes after Dan it is Ruiz who masterminds the plan to humble the Internal Affairs Assistant Chief and clear Dan. Lt Ruiz does not appear in the season finale but her last line in episode 19 is, "Everybody back to work. Let's go bust some punks.""
Diana Maria Riva has been paying her dues for a while now. She starred in Common Law on ABC in 1996 but like so many shows it was cancelled after a few episodes. This marks the third series where she has appeared with Bradley Whitford, The West Wing and Studio 60 On The Sunset Strip being the others. I love Studio 60.