Not long after the death of his father, Charles Koch, then in his early 30s, discovered a letter the family patriarch had written to his sons. "You will receive what now seems to be a large sum of money," Fred Koch cautioned. "It may either be a blessing or a curse." Fred's legacy would become a blessing and a curse to his four sons-Frederick, Charles, and fraternal twins David and Bill-who in the ensuing decades fought bitterly over their birthright, the oil and cattle-ranching empire their father left behind in 1967. Against a backdrop of scorched-earth legal skirmishes, Charles and David built Koch Industries into one of the largest private corporations in the world-bigger than Boeing and Disney-and they rose to become two of the wealthiest men on the planet.