MADRID, Spain (CNN) -- Spain's King Juan Carlos, with 32 years on the throne, turns 70 Saturday. But after years of undeniable adulation among Spaniards for putting down an attempted coup in 1981, he's recently faced more difficult times.
Widely respected in Spain since the beginning of his reign, Juan Carlos has recently faced criticism.
Small groups of leftists have burned his photo, and fiery criticism has also come from the right with one leading conservative radio host calling for him to abdicate.
Juan Carlos fired back with a rare public defense of his reign in a recent speech at the University of Oviedo in northern Spain.
"It's been the longest period of stability and prosperity in Spain ever in a parliamentary monarchy," the king said.
Juan Carlos was born on Jan. 5, 1938, in Rome and came to Spain as a boy to be educated under the right-wing dictator Francisco Franco, in a deal between Franco and Juan Carlos's father, Juan de Borbon, who led the Spanish royal family in exile, in Portugal.
When Franco died in 1975, Juan Carlos became king and, to the surprise of many, started steering Spain toward a democratic transition.
That was severely put to the test on Feb. 23, 1981, when rebellious Civil Guard troops stormed Parliament, firing shots into the ceiling while lawmakers and members of the elected government ducked for cover.
But Juan Carlos, from his small palace on the outskirts of Madrid, quickly began calling military commanders across the nation, and later made a nationally televised address, in military uniform, ordering troops to remain loyal to the new democratic constitution. The right-wing coup attempt failed.
"Juan Carlos won the right to be king that night, and all Spaniards accepted the monarchy, from that moment, without hesitation," journalist Julia Navarro, who was trapped in Parliament that night in the press gallery, recently told CNN.
For a quarter of a century, the king was almost untouchable. But now, as he turns 70, times have changed.
Last summer, a Spanish satirical magazine, El Jueves, caused a stir by depicting on its cover the king's son and heir to the throne, Crown Prince Felipe, explicitly having sex with his wife, Princess Letizia.
Soon after, small groups of leftists who favor independence for the Catalonia region around Barcelona, burned the king's photo at rallies, criticizing him as a symbol of Spanish unity.
From the right, radio host Federico Jimenez Losantos -- whose popular program is heard on the COPE radio network run by Spain's Roman Catholic church -- called for Juan Carlos to abdicate in favor of his son.
Jimenez Losantos recently declined CNN's request for an interview to explain his comments.
Last October, the king's speech at the University of Oviedo sought to remind Spaniards of the worth of this parliamentary monarchy --- in which the king is the head of state but holds no executive power under the Constitution of 1978, which was overwhelmingly approved in a national referendum.
Spain is a country that has had a long history of on-again, off-again friction with its royal family, including the declaration of a republic in 1931 that sent Juan Carlos's grandfather, King Alfonso XIII, into exile in Rome.
Juan Carlos has lately been in an uncustomary spotlight for other reasons as well.
At a contentious summit last November of Latin American nations along with Spain and Portugal, he told controversial Venezuelan President Hugo Chavez, "Why don't you shut up?"
The blunt talk from the king, seen on television, came after Chavez had harshly criticized a former Spanish prime minister and then interrupted Spain's current prime minister, who was trying to defend his predecessor.
Soon after, the king's oldest child, Princess Elena, separated from her husband after 12 years of marriage. It was the first marital problem made public in this royal family.
Polls show the king remains Spain's most esteemed man, but historian Santos Julia told CNN the aura around the king is showing cracks.
"The king's 70th birthday coincides with a public discussion about the role of the crown and the royal family that was not common earlier," Julia said.
He and others predict the king and royal family could now start to get the kind of media scrutiny that Britain's royal family has long weathered.
The Spanish royal household declined to comment, as is customary, on the significance of the king's 70th birthday, other than to say that Juan Carlos expects to spend the day with his family.
That was not the case just a few days ago, when he made a surprise New Year's Eve visit to Spanish peacekeeping troops in Afghanistan. E-mail to a friend