Greatness comes in the cloak of humility, Samuel Butler once wrote. He may well have been describing Avul Pakir Jainulabdeen Abdul Kalam. As principal scientific adviser to the prime minister, a cabinet-rank post he retired from in November last year, Kalam was entitled to a palatial bungalow in Lutyens' Delhi. Yet he chose to occupy two rooms in a Defence Ministry guest house that had been his home even when he headed the DRDO between 1992 and 1999.

BUDDHA'S BLESSING: Kalam (second from left) with Vajpayee and others at Pokhran

But such is the irony of fate that if all goes according to the NDA's plan, by July Kalam, a bachelor, will move into the country's most coveted piece of real estate-Rashtrapati Bhavan.

Kalam, who prefers bush shirts to suits and chappals to shoes, will have to get used to other prerequisites of power: formal wear for state dinners. Back in 1980, when the late prime minister Indira Gandhi called him to Delhi to personally felicitate him for putting the country on the world's space map, Kalam was in a panic as he owned neither a suit nor shoes. Satish Dhawan, the then head of the ISRO, told him, "You are already wearing the suit of success. So just be there."

Kalam's suit has been well-earned. Not only was he responsible for building India's first satellite launcher, the slv3, but in the 1980s he also made the country a missile power by developing the Agni and Prithvi. His role in 1998's Pokhran blast came in a decade devoted to weaponising nuclear capability.

If the Bharat Ratna in 1997 was a token of the nation's appreciation, the presidential nomination is the real thing. For those who ask why Kalam, the question really should be why not. For who can be a better candidate than a poor boat owner's son, whose sister had to pawn her jewellery to send him to the Madras Institute of Technology for a diploma in engineering?

It must irk Kalam that there are many who say he has been nominated entirely because of the religion he was born into. Kalam prays twice a day but religion to him has always been an intensely individual quest. He refers to the Bhagvad Gita as often as he does to the Koran. It was the Gita he quoted when he met reporters in Chennai after his nomination was announced. His spartan study has books on several religious philosophies.

He was there discussing the doctoral thesis of a student when Prime Minister A.B. Vajpayee called to inform him of the NDA's decision. All Kalam said then was that he was "overwhelmed" by the decision.

Though soon to be 71, Kalam displays remarkable energy, working late into the night and waking up early to go for a two-hour walk. It is his spartan habits-he is a vegetarian, teetotaller and has never smoked-that allow him to be constantly alert.

In Kalam's worldview there is no room for complexities. India lost its greatness, he believes, because in the past she became technologically inferior. So to regain it, India must be self-sufficient in science. If that sounds distinctly Nehruvian, Kalam's view on the atom bomb, which he helped build, is vastly different. He believes that such arms deter other nations from attacking or subjugating India and are, therefore, "weapons of peace".

His hobbies are calming: playing the rudra veena and writing poetry. It is this innate pacifism which stood him in good stead when he could not take up an assignment at the Indian Institute of Science, Bangalore, after conservative academics raised questions about his lack of a doctorate degree.

There are no such questions in his native Rameswaram, where his house on Thittakudi's Pallivasal Street is a testament to what Arun Tiwari, the co-author of his biography Wings of Fire, calls, "the best example of the meek inheriting the earth".

-Raj Chengappa with Arun Ram and Amarnath K. Menon