Position: General Secretary of the Socialist Party

Date of Birth: July 17, 1961

Candidate for prime minister at Oct. 4 2015 general election

Incumbent prime minister: Pedro Passos Coelho

Key facts:

-- Costa was mayor of Lisbon from July 2007 until April 2015, when he stepped down to run for prime minister. He was a popular mayor of Portugal's capital, where he was re-elected in 2009 and 2013, when he won a majority. He was in charge of the city during a growing tourist boom in recent years and also reduced the city's debts.

-- He challenged the incumbent Socialist leader, Antonio Jose Seguro, in a September 2014 ballot and won the party leadership with 68 percent of the vote. The party elected him in the hope that he would have a better chance of winning the premiership than Seguro.

-- The center-left Socialist Party's campaign under Costa has focused on returning disposable income to families hit by austerity under the debt crisis. He has said he would ease austerity and reverse a hugely unpopular increase in sales tax on restaurants at the same time as meeting Europe's debt and budget deficit goals.

-- Costa was interior minister in Prime Minister Jose Socrates' first government, from March 2005 until he stepped down to run for mayor of Lisbon. He was seen as being the right hand man of Socrates, who was imprisoned last year on suspicion of corruption and tax evasion. Costa's links to Socrates have been a theme of the campaign and he has tried to distance himself from the former prime minister.

-- Costa's first role in a Socialist government was as minister of parliamentary affairs under Prime Minister Antonio Guterres between 1997 and 1999. He became justice minister in 1999 until 2002.

-- Costa studied law in the 1980s in Lisbon, when he first entered politics and was elected as a Socialist deputy to the municipal council. He later took a post-graduate degree in European Studies and was a lawmaker in the European Parliament between 2004 and 2005. Costa practiced law briefly from 1988, before entering politics full-time.

-- Costa's father was Goan writer Orlando da Costa, a militant in the Communist party, and his mother, Maria Antonia Palla, was a journalist and women's rights advocate. His half-brother Ricardo Costa is director of weekly Expresso.

-- He married Fernanda Maria Goncalves Tadeu, a teacher, in 1987 and has a daughter and a son.

(Reporting by Axel Bugge , editing by Andrei Khalip)