Utilize the input text as a context reference, choose the right relationship between 'Syriza' and 'Alexis Tsipras' from the options.
Options: chairperson, subsidiary, 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