He did not specify where Marulanda died, though military officials say his death coincided with bombings in southern jungles where he was believed to be holed up.
A leathery-faced man with piercing eyes and a sixth-grade education, Marulanda was the world's longest-fighting rebel leader, the archetypal product of Colombia's bloody modern times.
He took up arms in his late teens and spent his entire adult life organizing resistance to governments he considered corrupt.
Famously reclusive and paranoid, Marulanda was never known to have gone abroad or even visited Bogota, Colombia's capital.
Jimenez said Marulanda's death followed a short illness whose nature he did not describe.
The guerrilla leader spent his last moments "in the arms of his companion, surrounded by bodyguards," Jimenez said. Marulanda fathered at least seven children but is not known to have married.
The FARC has suffered a series of setbacks in recent months, including the killings of two other members of its seven-man ruling Secretariat.
Born Pedro Antonio Marin, Marulanda took his nom-de-guerre from a labor leader beaten to death in the 1950s in a secret police dungeon. A master strategist, he earned his nickname "Tirofijo," or "Sureshot," for his skill ambushing army patrols.
Unlike other Latin American guerrilla movements, his survived as the Soviet Union collapsed and Cuba's military influence shrank. Colombia's lucrative drug trade was the enabling engine.
Marulanda's story personifies the political violence that has plagued Colombia since the late 1940s. A farmer's son born in the small southwestern coffee town of Genova, Marulanda took up arms in 1949 after Conservative Party henchmen began slaughtering supporters of the peasant-backed Liberal Party.
"The violence came after me like a shadow, from one town to the other," Marulanda told biographer Arturo Alape. Over a decade, at least 200,000 people died in political bloodletting that became known as "La Violencia."
When other Liberal guerrillas disarmed in 1953, Marulanda joined up with communist outlaws. Eleven years later, he co-founded the FARC after U.S.-backed government troops overran the isolated agrarian enclave that he and other communist refugees called home.
In the early 1980s, FARC negotiations with the government of President Belisario Betancur led to the creation of a legal rebel political arm called the Union Patriotica. But a truce dissolved in 1984 after a series of assassinations of party leaders, blamed on right-wing death squads.
In all, at least 4,000 Union Patriotica activists were killed, decimating the party and helping explain the FARC's subsequent refusal to disarm.
An avid student of military history and guerrilla warfare, Marulanda was also a tango lover who played violin as a child.
He built the rebels into a 15,000-strong guerrilla army that controlled vast swaths of countryside by the mid-1990s, dealing punishing blows to the military with attacks in which it captured scores of soldiers and police.
The government says the rebels currently hold some 700 hostages, including three U.S. military contractors and the French-Colombian Ingrid Betancourt, who the FARC kidnapped in 2002 while she was running for president.
Over the years, the army branded Marulanda a dangerous terrorist, offering princely rewards for his capture and periodically claiming they had killed him in combat. In his 1989 biography, Alape counts 17 such claims.
But time and again, Marulanda reappeared alive and well - dressed in simple farmer's clothing or camouflage fatigues and always with the trademark rubber boots, machete on his belt and towel draped over his shoulder to wipe the sweat off his brow.
Alfonso Cano, the FARC ideologue named to replace Marulanda, once said that after a long rainy march in the jungle he asked Marulanda how it was that his boots and pants had no mud stains.
"He told me, 'I never take a step without deciding where I am going to step next,"' Cano recalled.
As the FARC stepped up kidnappings and got deeper into Colombia's cocaine trade in the 1990s, Marulanda insisted the group had not shed its ideal of a more equal distribution of land and wealth.
The closest the grizzled rebel chief came to fulfilling that dream came with the 1998 election of President Andres Pastrana. Shortly after taking office, Pastrana pulled government troops from a rebel-dominated region the size of Switzerland, to facilitate peace negotiations.
The FARC began running the region as its own mini-state, raising taxes and appointing mayors. The peace process brought Marulanda into contact for the first time with scores of visitors - from Colombian politicians to U.N. envoys and American business executives.
On one occasion, Marulanda exchanged hats and an embrace with America Online founder Jim Kimsey.
Marulanda eschewed interviews, particularly with U.S. journalists that he suspected could be spies. He was so wary of assassination attempts that he would have his companion, "Sandra," taste his food to make sure it wasn't poisoned.
At the peace talks' January 1999 inauguration, he left Pastrana alone onstage next to an empty chair, claiming he'd gotten wind of an assassination attempt. Pastrana said he later learned Marulanda didn't want to be seen embracing the Colombian president.
The peace talks collapsed in February 2002 after the rebels hijacked a plane, kidnapping a senator on board.
President Alvaro Uribe's subsequent landslide victory drastically altered the military landscape. Backed by billions of dollars in U.S. aid, Uribe built up the armed forces and, making defeating the FARC his priority, pushed the rebels deep into Colombia's jungles.
The government now estimates the FARC's strength at about 9,000 fighters.