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

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