Nguyen Cao Ky was a young officer when he took part on the coup that led to Diem's demise. The subsequent games of power within the military junta propelled Ky to the position of Prime Minister, which he held between 1965 and 1967. That year he run for Vice President in a compromise ticket with Nguyen Van Thieu bidding for the presidency. Even though he had renounced to his own candidacy for the highest office under an agreement guaranteeing him a seizable share of power, he was outsmarted by Thieu, who accumulated power on his own Office.

In 1971, Ky again challenged Thieu on the elections, but was forced to withdraw his candidacy. He finally fled to California in 1975, after the fall of Saigon.

Letter from Ambassador Taylor to Ky
From the Historian of the State Department
http://www.state.gov/www/about_state/history/vol_iii/030.html (Doc. #37)

Ky, Thieu and the other young officers that ousted Khanh were increasingly upset with the U.S. Ambassador, General Maxwell Taylor. Taylor showed few diplomatic skills in his dealings with the South Vietnamese leadership, being at times insensitive to their domestic situation, and sometimes outright patronizing. In this letter, dated July 1, 1965, Taylor dictates--in humiliating detail--what course of action the U.S. expects from for the Vietnamese Government.