What is the relationship between 'Syriza' and 'Alexis Tsipras' in the context of the input sentence.
Options: employer, chairperson, parent organization, creator

Greek Prime Minister Alexis Tsipras tried to rally his Syriza party before a vote in parliament today (22 July) on the second package of measures demanded by international creditors to open talks on a new bailout deal.
chairperson