John D. Rockefeller was important due to his role in the creation of the oil trade monopoly called Standard Oil Company. He was highly successful and became the first American billionaire.
John D. Rockefeller developed a mind for business in his early age, keeping his own financial records at age 16. He saved the money he made with his early employments, and his father gave him a loan which allowed him to invest in a partnership with a former classmate named Maurice B. Clark. They entered into the oil business with Samuel Andrews, who owned a refinery. They provided the knowledge of trade, while he worked with the refinery. The business grew and was eventually sold to Rockefeller, who kept Samuel Andrews as a partner.
The company eventually grew very successful, acquired new partners and business methods and was renamed the Standard Oil Company. They made an agreement with a transportation alliance called the South Improvement Company that allowed them to eliminate their smaller competitors and turn the Standard Oil Company into a monopoly. His aggressive business practices made his company wildly successful at the cost of destroying other companies in the oil business. He was criticized greatly for his brutal and blatant attempts to remove his competitors, although he made vast contributions to education programs and medical research in his later years.