• Anthony "Tony" DiNozzo (Michael Weatherly) is a Senior Special Agent of the Major Case Response Team at NCIS. He is a former Peoria, Philadelphia, and Baltimore police officer and detective. After working on a case with Gibbs while he was a detective with the Baltimore Police Department, he discovered his best friend and partner was a dirty cop and quit from the police and joined NCIS in 2001.[16] Ducky considers DiNozzo to be a younger version of Gibbs, using his "gut" to solve cases (e.g., in the episode "Collateral Damage").[17] He is considered a notorious womanizer, his behavior even irritates the women he works with, although his behavior has been shown to change as the character developed. Despite this preconception about DiNozzo he is shown to not be the "womanizer" that his character is presented as within some conversations with his father (often referred to as "Senior").[18] DiNozzo is a movie enthusiast and often uses movie references when discussing a case, which annoys and irritates his coworkers.
• Abigail "Abby" Sciuto (Pauley Perrette) is a forensics specialist working with the Major Case Response Team. She has an affinity for goth fashion and a passion for Caf-Pow, a fictional high caffeine beverage. She has a close friendship with McGee, and claims to be Gibbs' favorite.[19]
• Timothy McGee (Sean Murray) is a Special Agent on the Major Case Response Team. He has a degree in computer forensics from MIT and a degree in Biomedical Engineering from Johns Hopkins, and, along with Abby Sciuto (with whom he was briefly intimate and remains close friends), acts as the team's technology specialist. McGee was originally assigned to the Norfolk Naval Base, but became a permanent team member at the end of the season two opening episode, "See No Evil". He is often called "Probie" by DiNozzo despite no longer being a probationary agent. Under the pseudonym Thom E. Gemcity he is also the author of a best-selling book using characters based on members of the team.