Rajnath Singh, under whose stewardship the Bharatiya Janata Party has stormed to power with its highest-ever tally, took charge as the Union home minister.
The 62-year-old Singh, who was elected from the Lucknow Lok Sabha constituency, has succeeded Sushilkumar Shinde in the crucial ministry that handles the country's internal security and the task of guarding its international borders with Pakistan, China, Bangladesh, Nepal and Bhutan.
Before assuming charge, Singh paid floral tributes to the country's first Home Minister Sardar Vallabhbhai Patel at his statue near Parliament.
He was welcomed with flower bouquets by a number of senior ministry officials led by Union Home Secretary Anil Goswami.
"The contribution of Sardar Patelji to the unity of the country has been tremendous. Country cannot repay what he has done for (it). Sardar Patel was the first home minister of the country and I came here to take his blessings before taking charge," he told reporters.
Meanwhile, Kiren Rijiju also took charge as the minister of state for home affairs at his North Block office.
Among the immediate issues that Rajnath, the teacher-turned politician, will have to deal with are tackling Naxal violence, activities of terrorist outfits in the country's hinterland, infiltration from Pakistan, illegal immigration from Bangladesh and strengthening intelligence gathering mechanism.
As home minister, two-term BJP president Rajnath will be part of the Prime Minister Narendra Modi-led Cabinet committee on security, the country's highest decision-making body on security matters.
Singh is bringing with himself his varied experience of handling crucial administrative assignments in a long political career, which has seen him serve, among others, as the chief minister of Uttar Pradesh and the Union minister of transport and agriculture in the Atal Bihari Vajpayee-led National Democratic Alliance government.
It was under Singh that Vajpayee's dream project -- the National Highway Development Programme was launched. He was also the education minister in the Kalyan Singh government in Uttar Pradesh.
Singh, who taught physics at a college in Gorakhpur in his early career, earned the reputation of being an able administrator in his roles of Union minister and the chief minister of Uttar Pradesh.
He has emerged from the ranks as a political heavyweight in the party largely due to his proximity to Rashtriya Swayamsevak Sangh, BJP's spiritual mentor.
Born on July 10, 1951, at Bhabhaura village in Uttar Pradesh's Chandauli district, Singh obtained an MSc in Physics from the Gorakhpur University and was appointed lecturer in the K B Post degree college in Mirzapur in 1971.
His association with the RSS began in 1964 when he was only 13 years old. Even as a lecturer he remained attached to the Sangh.
Rising step by step, he began his political innings with BJP's student wing, Akhil Bharatiya Vidyarthi Parishad, in 1969 as its organising secretary in Gorakhpur and rose to become the secretary of the then Bharatiya Jan Sangh's Mirzapur unit in 1974.
During the Emergency, Singh joined Jaiprakash Narayan's movement and was arrested in July 1975 before being released in 1977.