Step 1: Historical background.
Ho Chi Minh was a Vietnamese revolutionary leader and the first Prime Minister and President of the Democratic Republic of Vietnam. After World War II, he played a key role in establishing the first government in Vietnam.
Step 2: Analyzing the options.
(A) Ho Chi Minh: Correct — he established the first stable government in Vietnam.
(B) Bao Dai: A former emperor, later associated with French-backed government.
(C) Ngo Dinh Diem: Became leader later, not the first.
(D) Sihanouk: He was associated with Cambodia, not Vietnam.
Step 3: Conclusion.
Thus, the first government in South Vietnam was under Ho Chi Minh.