India's first-ever national security adviser Brajesh Mishra passed away Friday night at a private hospital in the national capital. He was 84.

As the news of his death just a day before his 85th birthday came, there was a buzz in the social online media, with several condolence messages pouring in.

"Brajesh Mishra RIP - a titan amongst Indian diplomats," tweeted Ministry of External Affairs spokesman Syed Akbaruddin.

"He (Mishra) died in a hospital," a government official told IANS.

A retired Indian Foreign Service officer, Mishra was a key aide of then Prime Minister Atal Bihari Vajpayee from 1998 to 2004.

He was also appointed the country's first national security adviser (NSA) in November 1998 and remained in that post till May 2004.

As principal secretary to the prime minister, Mishra was considered the most powerful officer in the then National Democratic Alliance government.

He brought to the office of NSA his expertise in diplomacy and geopolitics. He shaped the Vajpayee government's nuclear policy following the May 1998 tests, as also its foreign affairs initiatives, particularly with Pakistan.

As a career diplomat, Mishra was India's ambassador to Indonesia, and permanent representative to the United Nations from June 1979 to April 1981.

Before joining the Vajpayee government, he was part of the Bharatiya Janata Party's foreign affairs cell from 1991 to 1998.

However, he was known to have a mind of his own and did not strictly follow the BJP's views on all matters.

His views on the India-US civil nuclear deal, at variance with the BJP's, came to the fore, particularly, when he backed the United Progressive Alliance (UPA) government on the issue in 2008, both before and after the Manmohan Singh government faced a crisis following withdrawal of outside support by the Left parties.

However, Mishra was critical of the Manmohan Singh government in April this year after then Indian Army chief General V.K. Singh went to the Supreme Court over his birth date row, going to the extent of calling for the officer to be sent on forced leave.