What is the relationship between Syriza and Alexis Tsipras in the context of the input sentence. Choose an answer from: product/material produced; manufacturer; distributed by; industry; position held; original broadcaster; owned by; founded by; distribution format; headquarters location; stock exchange; currency; parent organization; chief executive officer; director/manager; owner of; operator; member of; employer; chairperson; platform; subsidiary; legal form; publisher; developer; brand; business division; location of formation; creator.

ATHENS, Sept 20 The leftist Syriza party of Alexis Tsipras has won 35.54 percent of the vote in Sunday's Greek national election based on 50 percent of votes counted, the Interior Ministry said on its website.
chairperson