What is the relationship between 'Syriza' and 'Alexis Tsipras' in the context of the input sentence.
Options: developer, subsidiary, chief executive officer, chairperson

Greek Prime Minister Alexis Tsipras was on Wednesday mulling whether to hold early elections after the austerity bailout split his radical left Syriza party, leaving him powerless to push further reform bills through parliament.
chairperson