Final answer:
King Tribhuvan was dissatisfied with being a figurehead under the Rana regime and played a critical role in the 1950 revolution by supporting the Nepali Congress Party. After the successful revolution, he returned as a constitutional monarch with more genuine authority.
Step-by-step explanation:
King Tribhuvan was not satisfied with his position because he was merely a figurehead with no real power under the Rana regime, which held the executive powers and controlled the government of Nepal. During the 1950 revolution in Nepal, King Tribhuvan played a significant role by aligning with the Nepali Congress Party and escaping to the Indian Embassy, which eventually led to the fall of the Rana oligarchy and the establishment of a constitutional monarchy. After the revolution, he returned to Nepal as a constitutional monarch, with a significant reduction in the autocratic power held by the king but with more genuine authority than during the rule of the Ranas.