Dack Rambo starred as Jack Martin Cole, who had emerged from an unjust three-year prison sentence (1975 to 1978) to become a rich playboy by day and a troubleshooting mercenary at night, à la The Saint.

Bert Rosario co-starred as Hector Ramirez, a former petty crook who was Cole's junior partner and former cell-mate, and Alex Courtney, another series regular, appeared as Arthur Woods, an attorney who had unsuccessfully defended Cole on criminal charges, who – from his involvement in that case – was motivated to head a special federal task force for the Justice Department to fight white-collar crime.

To that end, once he returned to prison after attending his dead parents' funerals, he learned how to crack safes, break into banks, and most of the other secrets of the criminal trade.

Upon his release, he decided to turn the tables on such above-the-law criminals as he blamed for his misfortunes by fighting them at their own game, à la It Takes a Thief, and using a unique way to leave his message: the "3" from a deck of cards, indicating how many years he spent behind bars.

The series was produced by Glen A. Larson, who later incorporated the ideas of the choice of a lead best known for daytime television and of a lone crusader protecting helpless, powerless, and/or innocent people against white-collar, above-the-law criminals into Knight Rider.