Refer to the input text as context and select the correct relationship between 'Syriza' and 'Alexis Tsipras' from the available options.
Options: subsidiary, chairperson, owner of, founded by

Greek Prime Minister Alexis Tsipras on Wednesday faced down a major mutiny in his radical left Syriza party and violent protests in the streets of Athens to win parliamentary approval for the tough reforms by creditors.
chairperson