Final answer:
Armand Hammer bought Occidental Petroleum in 1957, turning it into a major oil company in the international industry.
Step-by-step explanation:
The oil company that Armand Hammer bought was Occidental Petroleum. Armand Hammer was a well-known business manager and owner who, throughout his career, had various dealings in different industries, including oil. In 1957, Hammer gained control of Occidental Petroleum by acquiring a significant amount of its stock. His management and expansion of Occidental made it a major player in the international oil industry. Although the history of oil companies is vast and complex, with many political connections and influential figures, Armand Hammer's association with Occidental Petroleum stands out as a significant event in the industry's history.