He first tried to become president in 1974, losing an election that many believe was stolen from him amid allegations of fraud. Then in March 1982, he seized power after a military coup and began an 18-month reign during the bloodiest phase in Guatemala's 36-year civil war.
It was during this time that most of the hundreds of massacres against Maya Indians committed by the army were carried out as part of the U.S.-backed military's scorched-earth offensive against a leftist uprising based in the Mayan heartland.
Prosecutors argued during his trial that while in power, Rios Montt knew about and was responsible for the slaughter by subordinates of at least 1,771 people in the Quiche department of Guatemala's western highlands. They said the purported plan was to eliminate an indigenous Mayan ethnic group known as the Ixil in the towns of San Juan Cotzal, San Gaspar Chajul and Santa Maria Nebaj.
Rios Montt's administration is remembered for its ferocious counterinsurgency campaign, for faceless judges who held summary trials for those considered subversives and for the televised moralist and religious messages the dictator shared with the nation every Sunday night.
"The man who has two women is a pig; the woman who has two men is a hen," he told Guatemalans in one nationwide broadcast.
He was himself deposed by a coup in August 1983. He had sown discord with a wide swath of Guatemalans army leaders angry over his promotion of young officers in defiance of tradition; businessmen and the middle class upset by the creation of new taxes; Roman Catholics put out by his ignoring a request for clemency from Pope John Paul II on behalf of several prisoners sentenced to death.
A born-again evangelical Christian, Rios Montt also refused to bow before the pope during his visit to the predominantly Catholic country in 1983.
In an ironic twist, Rios Montt is the brother of Bishop Mario Enrique Rios Mont, who spells his last name differently and has headed the Roman Catholic Church's human rights commission in Guatemala.
Despite his tough rule, Rios Montt remained popular among many Guatemalans, especially in the areas hardest hit by the military offensive against guerrillas, due to his social welfare programs and the relative peace his "iron fist" approach brought to some regions.
During his trial, about 500 Ixil Mayans arrived in the capital to show their support in buses with banners that read "Do not shame the Ixil with that idea of genocide, because that's a lie."
The demonstrators arrived from Nebaj in the state of Quiche, an area where some of the worst massacres were carried out by the army.
But when Rios Montt was on trial this year, dozens of victims testified of surviving rapes, massacres and other atrocities as children, women and unarmed men were slaughtered in a "scorched earth" campaign aimed at eliminating support for a left-wing guerrilla movement.
Rios Montt's popularity among some groups was such that lawmakers in 1985 added a clause to the constitution banning him or any of his descendants from running for president. From that moment on, he worked on changing the law and on strengthening the Guatemalan Republican Front Party, a right-wing movement he created and formally registered in 1990. The party eventually changed its name to the Institutional Republican Party.
He made it back to government as a lawmaker in 1999, when his party won the presidency with Alfonso Portillo and a majority in Congress. His party appointed him congressional leader.
Rios Montt finally realized his dream of running for president again in August 2003. The Constitutional Court overturned several previous rulings and allowed his candidacy after tens of thousands of poor farmers sponsored by his party rioted in Guatemala City. But he finished far behind in third place, hurt partly by several corruption scandals during Portillo's government and increasing insecurity.
Despite a series of international inquiries finding him responsible for war crimes, Rios Montt served as a congressman for 15 years until he lost a re-election race in 2011. He held immunity from prosecution while a member of Congress and was put under house arrest after losing his post.
A judge charged him with genocide and crimes against humanity in January 2012. After the courts dealt with more than 100 appeals, the trial started this March.
The trial was widely seen as a turning point for a nation still wrestling with the trauma of a conflict that killed some 200,000 people.
The former general, who sat stiffly in court, impeccably attired in dark suits and well-shined shoes, steadfastly denied any guilt.
"I declare myself innocent," Rios Montt told the three-judge tribunal Thursday as many in the audience applauded. "It was never my intention or my goal to destroy a whole ethnic group."
"I never ordered attacks on a specific race. I never did it, and of everything they have said, there was no clear participation," he added.
The oldest of Rios Montt's three children, Homero, died in 1982 when guerrillas shot down the helicopter he was traveling in. His other son, Enrique, served in the army until his father's political party reached the presidency and he went into government as defense minister.
Zury, his only daughter and the youngest, followed her father's political career and was elected to Congress several times as a member of his party. She is married to a former member of the U.S. House of Representatives, Jerry Weller, a Republican from Illinois.