"I am still young and have full energy like any young man, even after last year's major heart surgery," the 68-year-old former Bihar chief minister told the media after celebrating his birthday on Thursday.
"I will put Bharatiya Janata Party and (Prime Minister) Narendra Modi in trouble during the assembly polls as I have regained my health," said the upbeat RJD leader.
He said he decided to project Nitish Kumar as the chief ministerial candidate of the alliance comprising Rashtriya Janata Dal, Janata Dal-United, Congress and Nationalist Congress Party to "stop the BJP from coming to power in Bihar".
The entire country is watching us and Bihar: Lalu
"The entire country is watching us and Bihar. The results of the assembly polls will prove to be the Waterloo for BJP and (prime minister) Modi," he said.
Lalu, who arrived here from Delhi, said he owned his good health to the blessings of the people, particularly his party's leaders and workers.
According to RJD leaders, a big cake was cut by party leaders here to mark Lalu's birthday.
RJD leaders said that his birthday was celebrated publicly ever since he became the chief minister of Bihar in the early 1990s.
"Laluji used to recall that he wasn't sure about the date he was born, though June 11 was mentioned as date of birth on his school certificate," an RJD leader said.