LUCKNOW, India — A Hindu warrior-priest has been chosen to rule India’s most populous state, and the cable news channels cannot get enough of him. Yogi, as everyone calls him, is so ascetic and incorruptible that he doesn’t use air-conditioners, they say. Yogi sleeps on a hard mattress on the floor. Yogi sometimes eats only an apple for dinner.

But the taproot of Yogi Adityanath’s popularity is in a more ominous place. As leader of a temple known for its militant Hindu supremacist tradition, he built an army of youths intent on avenging historic wrongs by Muslims, whom he has called “a crop of two-legged animals that has to be stopped.” At one rally he cried out, “We are all preparing for religious war!”

Adityanath (pronounced Ah-DIT-ya-nath) was an astonishing choice by Narendra Modi, India’s prime minister, who came into office three years ago promising to usher India into a new age of development and economic growth, and playing down any far-right Hindu agenda. But a populist drive to transform India into a “Hindu nation” has drowned out Mr. Modi’s development agenda, shrinking the economic and social space for the country’s 170 million Muslims.

Few decisions in Indian politics matter more than the selection of the chief minister of Uttar Pradesh, because the post is seen as a springboard for future prime ministers. At the age of 45, the diminutive, baby-faced Adityanath is receiving the kind of career-making attention that projects an Indian politician toward higher office.