The 47-year-old went on trial on Monday in Palma on the Mediterranean island of Mallorca for alleged embezzlement of public funds through the Noos Institute, a non-profit foundation he once chaired, to finance a lavish lifestyle.
His wife Princess Cristina stands accused of tax fraud in the landmark case - the first Spanish royal to face criminal charges in court since the monarchy was reinstated in the 1970s.
Gone are the cheerful pictures of him and his family that once lit up Spain's celebrity press, replaced by a morose-looking Urdangarin walking his dog in Geneva where he, Cristina and their four kids now live in exile, a supermarket bag tucked under his arm.
'The perfect boy'
It was a different story entirely in the 1990s when Urdangarin met then king Juan Carlos's youngest daughter.
Nearly two-metres (6.6-feet) tall, he charmed not only her but her family and much of the public.
Left-wing daily El Pais dubbed him "The perfect boy".
"Inaki is a good, good, very good man," his mother-in-law was quoted as saying in 2008 by a journalist specialising in Spanish royal affairs, Pilar Urbano.
"This is the image we Spaniards have all had, of an Olympic lad, clean, impeccable, good-looking, young, very in love with Cristina and a very good father," she said.
The praise betrayed no hint of the scandal that was brewing and erupted in 2011, severely denting the royal family's popularity.
Urdangarin was born on January 15, 1968, in the Spanish Basque Country, the second-youngest of seven children, to a Spanish father and Belgian mother.
He grew up mainly in Barcelona, where he also lived with Cristina following their lavish 1997 marriage that saw him bestowed the title of Duke of Palma.
The couple married in a lavish ceremony in 1997. Photo: AFP
After winning bronze medals with Spain's handball team at the 1996 and 2000 Olympics, Urdangarin retired from the sporting world.
He studied at Barcelona's ESADE Business School, where he met professor Diego Torres, the man who would become his associate... and then his worst enemy.
In 2004, Urdangarin became chairman of the organisation at the heart of the current scandal - the Noos Institute, a non-profit group he headed until 2006 with Torres as his right-hand man.
A whiff of scandal that same year -- when the couple reportedly spent some €6 million ($6.5 million) on a luxury house - soon dissipated in Spain.
Then in 2009, as the scandal was simmering in the background, Urdangarin and his family moved to Washington at the demand of his father-in-law the king, where he worked for Spain's telecoms giant Telefonica.
Why? asks Spain
But in 2011, the Noos case burst into the open with Urdangarin, Torres and others suspected of siphoning off money paid by regional governments to the institute for staging sporting events and conferences.
Urdangarin denies any wrongdoing, but the scandal led to a spectacular fall from grace and even precipitated the emotional abdication of King Juan Carlos in 2014 in favour of his son Felipe.
Since then, King Felipe VI has sought to distance himself from his sister Cristina and Urdangarin, and last year he stripped them of their titles of Duke and Duchess of Palma.
Madrid's waxwork museum has also moved Urdangarin's statue from its usual location with the rest of the Spanish royals to the sports hall.
But why did the man who "had it all" allegedly get involved in fraud.
"Some say that Inaki didn't want to be like the former husband of Princess Elena (Cristina's older sister), placed on company boards, but wanted to earn lots of money, be successful and prove to the royal family that he was a good guy," says royal affairs journalist Ana Romero.
But she adds other theories swirl around -- "that of an innocent man, not too intelligent, who fell into the hands of an unscrupulous man."
That of a "greedy" man. Or that of a novice "who started doing - awkwardly - what was being done around him."
By Laurence Boutreux / AFP