The Unfavourite: Not intentionally, but due to being a math child prodigy, Charlie required a lot more of their parents' attention when they grew up. Alan has some guilt about it and Don initially has some resentment, but they get over it.
Defective Detective: Charlie, a mathematical genius who uses his talents to help his FBI agent brother solve crimes, has emotional difficulties to the point that he locks himself in the garage to work on unsolvable problems when he can't deal with life. However, he overcomes this early on.
Bunny-Ears Lawyer: A very bright and valuable man; he even went into space once. However, he also sold his home out of not wanting to constrain himself and once had a diet of only white foods, among other quirks, such as staying in bathtubs for a long time.
Alan: I'm going to give you the same advice I give to all the geniuses I know.
Larry: And that is?
Alan: Don't be an idiot.
Larry: Ah. (nodding)
Amita Ramanujan (Navi Rawat)
Arranged Marriage: Amita was in one and knew the guy as a good friend since she was young. Her parents invited him back to try and win Amita over, though them and Charlie were unaware that he was gay, making the situation awkward but funny.
Fake Defector: Colby turns out to have been a triple agent for several years. This causes a fair bit of drama and angst, since the rest of the cast find out about the "defector" part well before they find out about the "fake".
Anti-Hero: Out of the FBI, Ian's the one most willing to use extreme means to complete his task, most apparent during "Ultimatum", and shows no hesitation in killing. He's still an overall a good guy, though.
Badass: You bet it! It sort of comes with being the fifth?.. Fourth?..Third best sniper in the country. He lives up to the reputation, too. If he's in an episode, he'll usually outshine the agents by being the one to take out the criminal of the week.