Analyze the relationship between 'Syriza' and 'Alexis Tsipras' within the context of the input sentence.
Options: chairperson, employer, chief executive officer, currency

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