In the context of the input sentence, determine the relationship between 'Syriza' and 'Alexis Tsipras'.
Options: owner of, manufacturer, industry, chairperson

Greek Prime Minister Alexis Tsipras on Wednesday had to face down a major mutiny in his radical left Syriza party, and violent protests in the streets of Athens, to win parliamentary approval for the draconian reforms demanded in the bailout package.
chairperson