Image copyright National Archives & Records Administration Image caption Everett Alvarez was given a hero's welcome upon his return to the US

The 1987 Vietnam War movie The Hanoi Hilton can be gruelling to watch.

It tells the true story of the American prisoners of war (PoWs) captured by the North Vietnamese. For years the imprisoned US servicemen were mentally and physically tortured.

Everett Alvarez, a former US Navy pilot who was held captive for eight and half years, was one of the film's advisers.

Meeting him today, it's hard to equate the agonising scenes in the movie with the impeccably dressed 76-year-old.

After retiring from the navy in 1980, Mr Alvarez went on to enjoy a high-profile government career.

If you don't truly believe in yourself and in the product, don't go for it. You have to be passionate about what it is you want to do Everett Alvarez

And for the past 26 years he has owned and run two successful IT and management consultancy businesses, including his current company, Alvarez & Associates.

But Mr Alvarez insists that his experience of being a PoW, horrific though it was, taught him invaluable lessons that he has applied to his life and work.

"It's about character," he says. "Character is the all-encompassing description of a person's moral sense of ethics, of responsibility, of commitment, of loyalty. It's a sense of personal integrity and honour.

"That's what's helped me, and I think it's also led to the personality of the company [Alvarez & Associates]."

Shot down

In 1964, Mr Alvarez, the grandson of Mexican immigrants, was a 26-year-old Navy pilot based on the USS Constellation aircraft carrier in the South China Sea.

On 5 August he was part of a bombing mission over North Vietnam sent in retaliation after a reported North Vietnamese attack a day earlier on two US destroyers.

Image copyright Naval History & Heritage Command Image caption Mr Alvarez rose to the rank of commander before he retired

The alleged attack (whether it actually took place was subsequently questioned) was known as the Gulf of Tonkin incident, and marked the start of a significant escalation of US military action in the Vietnam War.

Mr Alvarez's plane was hit and he ejected safely, only to be captured and taken to Hoa Lo Prison in North Vietnam's capital Hanoi, which American PoWs went on to sarcastically nickname the Hanoi Hilton, after the international hotel chain.

"Getting accustomed to captivity was difficult because I didn't know what to do," says Mr Alvarez, who was the prison's first US inmate. "The question was: how should I conduct myself?"

He decided on a course of resistance, refusing to aid the enemy even when their demands seemed relatively innocuous.

That resolve brought Mr Alvarez several times to the point of physical and mental breakdown, but he survived thanks to the mutual support of the other prisoners who communicated with each other by tapping on the prison walls.

"We had a philosophy that you didn't ever let your fellows down," he says. "If they couldn't take care of themselves you took care of them because you knew darned well they would do the same.

"And we had a goal. We were determined to come home with our personal integrity, our reputation, and with our honour."

Lifetime injuries

In 1973 Mr Alvarez and all other PoWs were released after the US agreed to withdraw its forces from South Vietnam.

Image copyright National Archives & Records Administration Image caption The American prisoners of war in the Hanoi Hilton looked out for each other

Mr Alvarez was awarded several military medals, and upon his return to the US became an overnight celebrity, which helped him form important political contacts.

When he retired from the Navy in 1980 - after reaching the rank of commander - he was asked to join the administration of then-US President, Ronald Reagan.

Still keen to serve his country, Mr Alvarez accepted the job of deputy director of the US Peace Corps, and then as deputy administrator of the Veterans Administration, which provides healthcare to former military personnel.

Image copyright US government Image caption Mr Alvarez worked for the Reagan administration for eight years

For five years he also took night classes to obtain a law degree.

"I came out of that prisoner of war camp after eight and a half years wanting to catch up," says Mr Alvarez.

"My whole life since then has been pursuing those dreams that I thought about as I was sitting in those cells. I've never looked back, always looked forward."

In 1988 Mr Alvarez left the Reagan administration to launch his first business, a management consultancy in Virginia.

Drawing on his eight years with the government, and the knowledge he had built up of public contracts, he decided he had the expertise to launch a company to bid for and win work with government departments.

In setting up the firm Mr Alvarez was helped by a government aid programme for disabled veterans. The years of torture and malnourishment had left him with nerve damage, and arthritis linked to the broken bones and other injuries he suffered.

In 2003 he sold this first business and a year later launched Alvarez & Associates.

In addition to management consultancy work the company manages IT contracts for the US government, and employs 28 people, many of whom, like Mr Alvarez himself, are military veterans.

It recorded $180m (£110m) in revenues last year, and Mr Alvarez says it is doing "comfortably."

'Understand your passion'

Throughout his business career Mr Alvarez has drawn on his experience of government contracts. His advice to young entrepreneurs is to equally discover their own niche or area of expertise and to fully embrace it.

Image copyright Getty Images Image caption Alvarez & Associates does IT work for the US government

"You must also have a real interest in the thing you want to build your business on - understand your passion and be willing to take a risk," he says.

"If you don't truly believe in yourself and in the product, don't go for it. You have to be passionate about what it is you want to do."

In spite of the high-profile government positions, and the respect he's earned for surviving his ordeal (only one other American was held for longer), Mr Alvarez says he doesn't take success for granted.

Image copyright National Archives & Records Administration Image caption Mr Alvarez came from a family of Mexican immigrants

"I still have to prove myself, so they [the customers] trust we can do a good job," he says. "It's still dependent on personal relationships.

"No matter how technical business becomes, depending on automation and technology, it still takes personal relationships to be successful.