Utilize the input text as a context reference, choose the right relationship between 'Syriza' and 'Alexis Tsipras' from the options.
Options: employer, currency, chairperson, chief executive officer

The Syriza party of former Greek prime minister Alexis Tsipras -- which came to power in January on a pledge to renegotiate terms of their international bailout but ultimately had to cave to creditor demands -- has a wafer-thin lead in the polls over the conservative New Democracy.
chairperson