Who will win in Israel Tuesday? Meet the unlikely kingmaker.

With Israelis heading to the polls for their second parliamentary election in a half year, an ultranationalist firebrand has emerged as a potential kingmaker who will decide whether Benjamin Netanyahu gets another term as prime minister or is replaced by a centrist challenger.

Avigdor Lieberman, an immigrant from the former Soviet Union and a former defense minister who heads the Yisrael Beitenu party, gained notoriety over the last decade as a hard-liner regarding Israel’s Arab minority and Palestinians in the West Bank and Gaza Strip.

But in elections last spring, Mr. Lieberman refused to join a right-wing coalition led by his former partner and old boss Mr. Netanyahu, citing a falling out over the influence of religious parties.

And in the campaign leading up to the vote Tuesday, the, politicians to promote religiously inspired policies.

The turning point“I don’t understand his agenda”Surprised supporters