1. Detective Mac Taylor played by Gary Sinise (Seasons 1-9)
He's the head of New York City crime lab, he's a CSI level 3 supervisor. He also lost his wife in the 9/11 attack.
2. Detective Danny Messer played Carmine Giovinazzo (Seasons 1-9)
He's a CSI level 3 and he's married to fellow CSI Lindsay Messer, they have a daughter together named Lucy.
3. Doctor Sid Hammerback played by Robert Joy (Recurring role in seasons 2-4 then made a main cast member in seasons 5-9)
He's the Chief medical examiner.
4. Adam Ross played by A.J. Buckley (Recurring role in seasons 2-4 then made a main cast member in seasons 5-9)
He's a lab technician.
5. Doctor Sheldon Hawkes played by Hill Harper (Seasons 1- 9)
Formly a medical examiner, he eventually became a CSI. He's a CSI level 2.
6. Detective Don Flack played by Eddie Cahill (Seasons 1-9)
He's a homicide detective.