He hoped to succeed Indonesia’s longtime dictator. He ordered the kidnappings of pro-democracy activists. He was accused of atrocities during the ruthless military occupation of East Timor. He has said elections run counter to his country’s culture.

Even so, Prabowo Subianto has spent the past two decades trying his hand at democratic politics, donning different personas in multiple attempts to become Indonesia’s leader.

Now, a month before the next election, nearly every poll shows Mr. Prabowo, 72, leading in the first round of voting. His rise, with the help of a running mate who is the son of the popular departing president, Joko Widodo, has alarmed millions of Indonesians who still remember the brutal and kleptocratic rule of Suharto, Mr. Prabowo’s former boss and father-in-law.

A victory for Mr. Prabowo, his critics warn, would revive a dark past.

“What will happen is the death of democracy,” said Hendardi, the director of the Setara Institute for Democracy and Peace. Like many Indonesians, he goes by one name. “We have long been against Prabowo,” he added, “and with our limited power, we were still able to prevent him from moving forward. But now he has gained this support.”