Brennan was first mentioned in "" when the survivors listen to Danielle Rousseau's transmission. She mentions that she is in the radio tower and that "Brennan took the keys." He finally appears for the first time when he, Montand, Robert, and Danielle discover a time-traveling Jin stranded in the ocean. They rescue him and bring him to shore. (5x04) While traveling to the radio tower with the rest of his expedition, Brennan and the rest of the team were attacked by the monster, who killed Nadine and abducted Montand after ripping off his arm. Brennan, Robert, and Lacombe followed the monster into the hole. Some time afterwards, they presumably began to act differently due to the sickness, and were killed by Rousseau. Brennan's corpse, along with Lacombe's, was found on the beach by Jin, with three bullet wounds in the chest. (5x05)
In the official ABC press release for "", Brennan was credited as Frenchman #3.
"Brennan" is also the last name of Kate's childhood sweetheart, Tom.
It is interesting to note that the actor who portrays Brennan, Bruno Bruni, shares the first two letters of both his forename and surname with the character he portrays.
What are the keys Danielle mentions in the transmission?