With his father elevated to semidivine status, Thailand's Crown Prince Maha Vajiralongkorn will have a huge challenge not just to fill the shoes of King Bhumibol Adulyadej, but to define himself as the new monarch.

Tall and with a soldier's posture, the Crown Prince, 64, was schooled in England and attended Australia's Royal Military College at Duntroon, in Canberra.

He was invested as Crown Prince in 1972 by King Bhumibol.

The heir apparent took up his duties after returning to Thailand, serving in the Royal Thai Armed Forces and making frequent tours around the country, while representing his father at official events and ceremonies.

He reportedly led counterinsurgency campaigns against communists in Thailand in the 1970s.

He is also a qualified fighter pilot and regularly flies big jets.

As the Crown Prince, he had six battalions of elite troops under his command.

Among other things, he established hospitals in remote areas; by 1997, Crown Prince Hospitals had been set up in 21 locations.

The Crown Prince has been married three times. His first wife was first cousin Soamsavali Kitiyakara. The couple married in 1977 and have a daughter but they divorced in 1993.

He married a second time, to actress Yuvadhida Polpraserth, with whom he has five children.

In February 2001, the Crown Prince married, for a third time, to Ms Srirasmi Akharaphongpreecha.

The marriage was announced only in 2005, and she was given the royal title Mom Srirasmi Mahidol na Ayudhya by the King.

Her "simplicity, warmth win hearts," the English newspaper The Nation wrote.

A few months later, the couple's son Dipangkorn Rasmijoti, now 11, was born.

In November 2014, senior police officials related to Ms Srirasmi were found to have allegedly used their connections with the palace to extort and amass vast wealth, and her family was stripped of the royally bestowed surname. The couple divorced.

Media reporting on the monarchy is constrained by Article 112 of Thailand's criminal code - a harsh lese majeste law which punishes with a jail sentence of up to 15 years anyone deemed to have insulted the King, Queen, heir apparent and Regent.

But in 1987, in the course of an interview with the Thai magazine Dichan, the Crown Prince was asked how he felt when people talked about him "as if Your Highness was a black sheep".

His reply: "Sometimes, black sheep serve a purpose, one of helping others. Black sheep help those not-too-white ones seem whiter."

Occasionally, European newspapers have featured rare pictures of him in Europe, where he reportedly spends much time, specifically in Germany.

But in more recent years, as his father grew frail, the Crown Prince took over many more ceremonial duties including accepting the credentials of foreign ambassadors.

Diplomats who met him reported him to be well informed, affable and urbane.

Lately, he has been taking on a higher public profile. He led bicycle rallies in Bangkok separately for the King and Queen in August and December last year.

Themed "Bike for Mum" and "Bike for Dad", they were his first mass public events, and drew the enthusiastic participation of tens of thousands of middle-class Thais. The first event drew as many as 300,000 to register nationwide.

Security was tight for the rallies in Bangkok as the Crown Prince led cyclists - including the Prime Minister and Cabinet ministers - on the route, smiling and waving to hordes of well-wishers who turned out to see him.

Many of those who participated had bought bicycles specially for the occasion, while onlookers waited for hours in the heat to catch a sight of the Crown Prince.

Similar mass rides were conducted nationwide, in events pitched as a show of unity in a nation politically polarised over the last decade.