Short answers, pulled from the story.
Carlos Castillo Armas was a Guatemalan military officer who served as the 28th president of Guatemala from 1954 to 1957. He came to power after a CIA-backed coup overthrew President Jacobo Árbenz in June 1954, and was assassinated on the 26th of July 1957.
Operation PBSuccess was a covert CIA operation authorized by President Dwight Eisenhower in August 1953 to overthrow the Guatemalan government of Jacobo Árbenz, with a budget of between five and seven million dollars. Castillo Armas was chosen to lead the operation, commanding a force of 480 CIA-trained soldiers who crossed into Guatemala on the 18th of June 1954.
Castillo Armas returned 368,481 of the 529,939 manzanas of land expropriated under Decree 900 to the original large landowners. Thousands of peasants who tried to remain on their redistributed plots were arrested, and landlords used those arrests to carry out evictions.
The committee, known as the CDNCC, investigated nearly 70,000 people over the course of Castillo Armas's rule. Decree 59, passed in August 1954, allowed security forces to detain anyone on the CDNCC blacklist for six months without trial. The final list of suspected communists included one in every ten adults in Guatemala.
Castillo Armas was shot and killed on the 26th of July 1957 by Romeo Vásquez Sánchez, a member of his own presidential guard who held leftist sympathies. Vásquez approached Castillo Armas as he walked with his wife in the presidential palace and fired twice; Castillo Armas died instantly. Whether Vásquez acted alone or as part of a wider conspiracy was never conclusively determined.
The reversal of agrarian reform under Castillo Armas sparked leftist insurgencies beginning in 1960 that grew into the Guatemalan Civil War, a conflict lasting from 1960 to 1996 that killed 200,000 civilians. Ninety-three percent of atrocities against civilians during the war were committed by the US-backed military, including a genocidal scorched-earth campaign against the indigenous Maya population in the 1980s.