New Delhi: He made his name as a ruthless backroom politician and master strategist who won election victories for his boss, India's Prime Minister Narendra Modi. He also has a reputation for the incendiary, recently describing illegal Bangladeshi immigrants as "like termites" taking grain and jobs from India's poor.
Now, 54-year-old Amit Shah will have to demonstrate he has the temperament to run India's most sensitive cabinet portfolio, home affairs.
The brief includes internal security, border management, running armed police forces and keeping the lid on militancy in the troubled region of Kashmir - all with the potential to ignite or exacerbate communal tensions.
His supporters were in no doubt that he will frighten anyone who does not put Indian interests first.
"A brilliant strategist and an excellent administrator, his appointment as HM is bad news for forces inimical to the interests of India," tweeted the new minister for oil and steel, Dharmendra Pradhan.
BJP spokesperson Tajinder Pal Singh Bagga, also in a tweet, warned people in Kashmir who pelt the army and police with stones that they had better pack their bags now that Shah was in office.
Some Indian liberals were nervous about how Shah would respond to critics of the government and the BJP.
"Any form of disagreement with the government or with the idea of Hindu nationalism would now be presented as a form of dissidence," said Nilanjan Mukhopadhyay, an author of books on Modi and the Hindu right.
He would likely rule the ministry with "an iron fist", he added.
If he does succeed, Shah's reputation as an effective political operator and his close relationship with Modi means he will have huge influence in the government, and put him in a strong position to eventually succeed Modi, political strategists said.
Political operator
The son of a prosperous family in Gujarat, Shah left school around the age of 18, according to a declaration signed in the April-May general election.
Since then, aside from a short spell selling PVC tubing, he said in a 2016 interview, Shah has spent almost his entire adult life working for the BJP and its affiliated groups.
Shah, who has long been Modi's top strategist, helped rouse the BJP's base in the election, overcoming losses in key state polls last December and returning Modi with an improved majority.
A relentless politician, he has run 29 elections, from municipal bodies to parliament, and lost none. He travelled 150,000 km (93,200 miles) to address 161 public rallies during the election, he said earlier this month.
Shah's efforts helped to blunt voter discontent at a lack of job creation and distress about low farm incomes by portraying the opposition as weak and indecisive, at best, and at worst as appeasers of minority Muslims and arch-foe Pakistan - deftly exploiting national security fears.
"Modi and Shah work in tandem," said a BJP official who has worked closely with Shah, speaking before his appointment.
"They have been political associates for 30 years-plus," said a Gujarat state official. "They know each other's secrets, their's has been a relationship of mutual trust, and gains from the association."
Hardline views
Shah is known as a Hindu-hardliner with uncompromising views.
He mocked Rahul Gandhi, the chief of the opposition Congress party, for choosing to run in a Muslim-dominated constituency in the southern state of Kerala.
"When a procession is taken out there, it is difficult to make out whether it is an Indian or a Pakistani procession," he said.
Like Modi, Shah has faced accusations that he looked the other way as Gujarat's home minister in 2002, when mobs attacked and killed Muslims in revenge for the burning of Hindu pilgrims on a train in the worst sectarian bloodletting in independent India. Both have always denied wrongdoing.
Shah himself was acquitted in 2014 of separate charges levelled in 2010 over alleged extrajudicial killings.
He is now in a prime position to take over once Modi bows out when he turns 75 in 2025, a party rule the prime minister adopted to edge out older BJP leaders who had sought to resist his rise.
"It's some time off, but at the moment he is best placed to succeed him," Mukhopadhyay said.
