Augusto Pinochet, dictator of Chile from 1973 to 1990, took power in a US-backed coup d'état that itself happened after years of economic warfare between the US and Chile. After the overthrow of Allende, Chile's elected socialist President, the US immediately recognized the military junta's legitimacy and offered it support, both financial and technical.

Here is an archive of US documents discussing CIA involvement in the Chilean regime, both before and after the coup. Key quote:

Although CIA did not instigate the coup that ended Allende's government on 11 September 1973, it was aware of coup-plotting by the military, had ongoing intelligence collection relationships with some plotters, and—because CIA did not discourage the takeover and had sought to instigate a coup in 1970—probably appeared to condone it.

It should also be noted that Pinochet's economic policy was very much influenced by the liberal economic policy of Milton Friedman's Chicago School - most of the key economic positions (minister of Finance, head of the Central Bank) were held by Chicago alumni.

As for Pinochet's qualifications as a dictator, it's pretty clear-cut: he seized power through violent means and was afterwards the supreme ruler of the country until he stepped down in 1990. His regime was a violent, totalitarian one: according to various historians, during his 17-year rule, between 1,200 and 3,200 people were killed, up to 80,000 interned and as many as 30,000 tortured.

Carlos Castillo Armas was the dictator of Guatemala from September 1, 1954 – July 26, 1957. He was placed in power after the United States initiated PBSuccess in 1954.

Jacobo Arbenz was the elected president of Guatemala who strove for land reform. The United Fruit Company owned the majority of land in Guatemala but paid its workers poorly and paid minimum taxes. Arbenz took steps to expropriate the land owned by UFC. For restitution, Arbenz offered to pay UFC the money that UFC said their land was worth. Knowing they had been lying on their taxes for years, UFC claimed they were owed much, much more. Arbenz refused their counter-offer and UFC went crying to the American government.

The two most important players for the American were brothers: John Foster Dulles, the Secretary of State, and Allen Dulles, the director of the CIA. Both had major stakes in UFC. They convinced Eisenhower that Arbenz was taking land because he was a communist (he wasn't) and was working for Moscow (he wasn't). So Eisenhower authorized the CIA to ferment a military coup, which put Armas in charge.

When in power he cancelled Arbenz' land reforms, forbade presidential elections, only allowed his party to run for congressional office, and restored secret police in the country. He was shot by one of his guards in 1957.

If you're interested in this topic you may want to check out Overthrow: America's Century of Regime Change from Hawaii to Iraq by Stephen Kinzer. He also talks about Hawaii and Operation Ajax, which replaced the democratically elected president of Iran with a dictator.