||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.
||Alan Eppes, played by Judd Hirsch
Alan Eppes is the father of Don and Charlie Eppes. Alan is a widower, having lost his wife to cancer a few years earlier. He's a retired city planner for the City of Los Angeles. He currently has a small consulting business and audits classes at CalSci.
In the first season, he put the family's elegant craftsman style home on the market. Unbeknownst to him, it was Charlie that purchased it for the asking price. Alan still lives in the house with Charlie. He used some of the proceed to start his business. Alan is an accomplished cook and frequently makes dinner for Charlie and Don.
Alan is very proud of his sons, even though they are so different from one another, yet very much the same in some ways. Alan was very happy when Charlie started working with Don at the FBI, as they were doing something together and forming a common connection.
Alan is brought in occasionally to help out on Don's cases when his expertise in urban planning and city infrastructure is beneficial. He identified how the terrorists were going to poison the city water supply by accessing a crucial water main through the old Red Car tunnels that ran through Hollywood.
In the third season, Alan began dating Charlie's department chair, Dr. Mildred Finch. This led to some potentially awkward moments, but everyone seemed to work through them.
The only thing that seems lacking in Alan's life is the fact that he's unlikely to become a grandfather anytime soon.