Special Agent Mike Renko was a Field Agent assigned to the NCIS Office of Special Projects.
During an operation in "Legend Part 1" and "Legend Part 2" which acted as the series pilot for NCIS: Los Angeles, Special Agent Mike Renko acted as "Mattie Rae", a customer who wanted to buy weapons. He revealed his true identity as an agent after a gunfight that left an arms dealer and his two guards dead.
After that had happened, Macy tasked Agent Renko to tail Mossad Agent Michael Rivkin.
Later, Special Agent Leroy Jethro Gibbs joined Renko after tailing Rivkin into a hotel and watching him have coffee in the gazebo where they discovered the body of another member of the terroist cell that Rivkin had killed before fleeing the scene.
During an operation, armed with rifles, Renko, Sam Hanna, and Kensi Blye stormed the shop where the target was located. The operation was successful, resulting in the capture of the leader of the terrorist cell.
At a certain point, Agent Renko returned to OSP, having gone on an investigation for two months on a dangerous militia group called "Enhancing Law Enforcement", also known as "ELE", which fought illegal immigration ruthlessly.
Rumor had it that the ELE were going to steal the "Dragon" missiles. After his informer was killed by Marine Corporal Scott Riley, Renko joined the co-operation with G. Callen along with other members.
During the recon on Riley's vehicle, Kensi was attacked by Riley who intended to kill her by garroting her. She managed to fight back and got the upper hand in the battle before Riley escaped. Agent Renko, who just finished checking Riley's mail box, showed up and arrested Riley with Kensi.
Later, Renko, Kensi, and Sam tracked down the camp of ELE. After being captured by the militia, Sam contacted with Kensi via Morse code. Sam told them to use "Maskelyne".
After learning what "Maskelyne" stands for, Renko and Kensi opened fire from several locations, making the militia believe that they had been surrounded by multiple units.
At a certain point, Renko made an arrangement for Callen and Sam to meet Detective Matt Bernhart. The four later worked together on a fake bank robbing.
When Callen was absent, Renko was called to rejoin the team due to the lack of personnel and possible security concerns. He joined the operation to stop Ruman Marinov and his men from killing a German CEO.
He was shot during the mission but survived because of the bullet proof vest he was wearing at the time. Later, he joined the operation to catch Eugene Keelson.
After being absent for most of the three seasons, Renko returned in the Season 3 finale, "Sans Voir" where it was revealed that he was working with Assistant Director Owen Granger on a case but during a gunfight at a shop, Renko was shot in the jaw by a sniper. Despite efforts to save him, he eventually died after his surgery, leaving the entire team devastated and causing Hetty to realize that it was The Chameleon who was responsible for the whole thing.