||Don Eppes, played by Rob Morrow
Don is the eldest of the Eppes brothers. He is a Senior Special Agent in Charge in the FBI field office in Los Angeles. He grew up in Los Angeles and transferred back home when his mother became ill with terminal cancer two years prior to the beginning of the series. His previous assignments included Quantico and Albuqurque NM.
Don grew up in the shadow of his mathematically gifted brother Charlie, despite being 5 years older than Charlie. Charlie was very advanced and put ahead in school resulting in the brothers being in the same graduating class in high school.
Don attended college on a baseball scholarship and played minor league baseball for the Stockton Rangers for a year or so.
Don has enlisted Charlie to assist him with difficult FBI cases where Charlie's mathematical prowess proves quite valuable. Unfortunately this does result in conflicts based on events that happened years ago. They always manage to work out their differences to solve the case at hand, but occasionally some issues remain unresolved. If anything, their working relationship has brought them closer together and able to understand one another better, much to the relief of their doting father, Alan.
||Charlie Eppes, played by David Krumholtz
Charlie Eppes was a child prodigy in Mathematics. He graduated from high school 5 years early. Ironically, he was in the same high school class as his older brother Don. Charlie had a difficult relationship with his brother during high school.
After high school, Charlie attended Princeton University. For the first couple of years, Charlie's mother moved to Princeton to watch over him. After completing his undergraduate work, Charlie stayed on at Princeton to get his PhD. It was at Princeton that Charlie met Dr. Larry Fleinhardt, who became his mentor and confidant.
After Princeton, Charlie joined the faculty of CalSci, near his home in Pasadena. It was at this time that Dr. Fleinhardt also joined the faculty at CalSci. It's unclear who instigated the move. Charlie returned home and lived with his parents in the elegant, Craftsman style house he grew up in. By this time, Don had joined the FBI and was assigned elsewhere.
All was going well until about 4 years before the series started when Charlie's mother was stricken with cancer and passed away. When he found out about his mother's illness, Don requested a transfer to the FBI's LA office. Charlie did not handle his mother's illness well. He withdrew into himself and spent endless hours in the garage writing on chalkboards futily attempting to solve an unsolvable mathematics problem.
After his mother's death, Charlie continued to live in the family home. He then started to assist Don with cases he was working on by applying mathematics to help resolve situations that appeared to be stuck at a dead end. Charlie is frequently called on by Don and other members of Don's team to consult on complex cases. Charlie is frequently assisted by Dr. Fleinhardt, Amita (a former student and now CalSci faculty member), and even his father, Alan.
Early in the series, Alan wanted to sell the house. Charlie wound up buying the house from him, but Alan didn't know that Charlie was the buyer until the last minute. Alan and Charlie continue to live in the house together. Don joins them for dinner frequently.
Charlie and Amita have recently developed a strong romantic interest, so Amita is a frequent dinner guest as well. Alan is hopeful that he will have grandchildren one day.