Rajya Sabha MP from the Janata Dal(United) and industrialist Mahendra Prasad died at a private hospital here, his party said on Monday.
The 81-year-old Prasad passed away on Sunday night after battling prolonged illness.
Estimated to be one of the richest members of Parliament, the founder of Aristo Pharmaceuticals was a seven-term Rajya Sabha MP from Bihar and was also elected to the Lok Sabha once.
Prime Minister Narendra Modi and Bihar Chief Minister Nitish Kumar were among those who expressed condolences at his death.
Modi said, "Saddened by the passing away of Rajya Sabha MP Dr. Mahendra Prasad Ji. He served in Parliament for many years and was at the forefront of several community service efforts. He always spoke for the welfare of Bihar and its people. Condolences to his family. Om Shanti."
Kumar said his demise is a big loss to the society and politics besides industry.
Prasad was first elected to the Lok Sabha on a Congress ticket in 1980. He remained associated with the party for a long time and shifted his loyalties later as its fortunes declined in the state.
He joined the Janata Dal and then its offshoots, first Rashtriya Janata Dal and then JD(U).
His name was often prefixed with "King", a pointer to his vast fortunes and the fact that any change in the political weather in his home state mattered little to him as he remained in the Rajya Sabha since 1985 except for brief gaps.