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

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