In the context of the input sentence, determine the relationship between 'Syriza' and 'Alexis Tsipras'.
Options: director/manager, employer, owner of, chairperson

Left-wing Syriza party leader Alexis Tsipras speaks to his supporters at Syriza's partyâ€™s main electoral center in Athens, Sunday, Sept. 20, 2015.
chairperson