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

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