Catherine "Cath" or "Cat" Rollins was a former Navy Lieutenant in the United States and also a former intelligence officer who was originally assigned to the USS Enterprise and who is also the love interest/friend of Lieutenant Commander Steve McGarrett (2010).
She aided the H50 team before eventually joining them presumably on a permanent basis during Season 4 before departing the team and Hawaii for good in the Season 4 episode, Makani 'Olu a Holo Malie (episode) as she went off searching for a young boy who had been kidnapped by the Taliban.
Born to an unnamed mother and father in an unknown State, Catherine later chose to join the United States Navy, rising to the rank of Lieutenant.
At some point in her Naval career, she met Steve McGarrett with the two eventually becoming close and even lovers at some point.
Catherine made her debut appearance in Nalowale (episode) where she was revealed to be McGarrett's girlfriend with the two even spending the night together in Steve's house.
In Makani 'Olu a Holo Malie (episode), after helping save a young boy and his family from the Taliban, Catherine rescued Steve from captivity and later sent him and Danny back to the United States, Catherine having chosen to stay behind in Afghanistan to help the young boy.
- Michelle Borth was originally a recurring guest star up until the Season 3 premiere, La O Na Makuahine (episode) where she was added to the opening, resulting in her becoming a series regular.