Spain's next prime minister could be a young pony-tailed university professor, or perhaps a leather-jacketed lawyer who once posed nude in campaign posters.

They demonstrate just how much Spanish politics has changed in the four years since the last general election.

A severe economic crisis, crushing unemployment and incessant corruption cases have turned many Spaniards away from the staid, career politicians who head the mainstream right and left parties that have alternated in office for decades.

Here's a look at the four politicians vying to become Spain's next prime minister:

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MARIANO RAJOY

At 60, the incumbent is the oldest candidate and the only one with time spent in government.

Chosen to take over the ruling right-of-center Popular Party in 2003 by then-premier Jose Maria Aznar, the tall, bespectacled and gray-bearded Rajoy has had his leadership abilities regularly questioned. He lost two elections to the Socialists, but his perseverance paid off when he won the last one, in 2011, with a whopping majority.

The son of a provincial judge, Rajoy studied law and became the country's youngest property registrar at the age of 24. A cycling and football fan, Rajoy acknowledges he reads little and prefers light sports publications to serious newspapers or literature.

As prime minister his main success has been pulling Spain back from an economic abyss and returning it to growth. But the austerity measures and labor and financial reforms that helped him to do that, together with his failure to create anywhere near the 3 million jobs he promised, have eroded his popularity. So has his decision to raise taxes after taking office in 2012, despite repeated promises during his 2011 campaign that he wouldn't.

The involvement of many current and former party members in corruption scandals has also tarnished his image.

A staunch proponent of law and order, Rajoy is the party leader most opposed to any negotiations with the pro-independence movement in the northeastern Catalonia, a stance many see as contributing greatly to the growth of a secessionist movement.

A close ally of the Roman Catholic Church, Rajoy has sided with church stands on abortion, euthanasia and religious education in public schools. He has also campaigned for tighter immigration controls and stirred criticism in 2007 when he dismissed the threat of climate change as exaggerated.

He is married with two sons.

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PEDRO SANCHEZ

Sanchez, 43, was unknown to most Spaniards until he was elected secretary general of the main opposition Socialist party in 2014. A former university economics professor, he joined the party in 1993, becoming a Madrid city councilor in 2004 and then a member of parliament in 2009. He worked as a party aide in the European Parliament and at the office of the U.N. High Representative for Bosnia during the war in Kosovo.

The former basketball player towers above most of his colleagues. He also stands out for being fluent in English and French, something of a rarity among Spanish party leaders frequently criticized for their inability to speak foreign languages.

Although Sanchez has helped unite his party since it was ousted as the ruling party in a 2011 landslide, he spends much of his time fending off criticism of his predecessors' policies. But while his decent guy image has definitely helped the Socialists, he often lacks luster and political punch, which probably explains why his party was second-placed but trailed the ruling conservatives by 8 percentage points in a recent well-trusted government-run poll.

Sanchez also has few outright enemies, making him a good option to receive outside support if needed to form a government.

He has promised to roll back several Popular Party laws, including a labor law that made it easier to hire and fire people, and a so-called "Gag Law" that sets stiff fines for some protests and allows authorities to fine those distributing unauthorized images of police.

He also favors negotiations to reform Spain's regional government structure to try to convince Catalan nationalists to abandon their campaign to break away from Spain.

Sanchez is married with two daughters.

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ALBERT RIVERA

Rivera, 36, is the rising star of Spanish politics and the one tipped with the best chance of edging both Rajoy and Sanchez to take office. A native of Barcelona, his popularity soared in the region surrounding Catalonia mainly due to his Ciudadanos party's ability to galvanize opposition to the surging Catalan independence push.

He entered the national race only a year ago and his mix of centrist, business-friendly policies, along with his pledged crusade against corruption, have struck a chord among many, especially young professionals.

The trusted government-run CIS final pre-election opinion poll placed him as Spain's most respected party leader.

A national debating champion in college, the telegenic and media savvy Rivera answers questions on every possible topic with ease and determination. A republican, although he respects the monarchy, he claims to represent a new pro-center generation tired of left and right ideologies.

However, some fear that his vagueness on some issues — such as economic policy, regional devolution, immigration and domestic violence — hide a right-leaning wolf in sheep's clothing.

Handsome and slickly dressed, he was probably best known for posing nude in some of his first election posters several years ago.

He helped found Ciudadanos after gaining his doctorate in constitutional law. He has been a lawmaker in the regional Catalan parliament since 2006.

Rivera is divorced with one child.

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PABLO IGLESIAS

Podemos leader Iglesias is a political science professor and the person who has caused the biggest stir in the Spanish political scene in recent years. He was something of a household name prior to the party's formation chiefly due to his calm but piercing rhetorical skills on one of Spain's most popular TV political chat shows, in which he lambasted the conservative government's policies and upstaged right-wing political and media opponents.

Hailing from the Madrid working class neighborhood of Vallecas, Iglesias, 37, sports a ponytail and prefers jeans and rolled-up shirt sleeves to his opponents' suits and ties. He champions slogans such as Spain is "run by the butlers of the rich."

A friend and supporter of Greece's leftist Prime Minister Alexis Tsipras, he also backed policies by left-wing governments in Venezuela, Bolivia and Ecuador.

Podemos has its roots in the 2011 Madrid street protests, in which people fed up with business and political corruption demanded a better, fairer democracy. The party surprised Spain's political establishment when it won five seats in the European Parliament elections in May 2014, just four months after its formation.

Some opinion polls last year suggested Iglesias could win the upcoming elections, but his allure has waned chiefly due to what some see as the repetitiveness and even softening of his anti-establishment political message, as well as his perceived attempts to impose views on party members.

Iglesias is single.