Analyze the relationship between 'Syriza' and 'Alexis Tsipras' within the context of the input sentence.
Options: brand, industry, chairperson, parent organization

ATHENS Aug 30 The leftist Syriza party of former Prime Minister Alexis Tsipras will challenge Greece's creditors on unresolved aspects of the nation's bailout but implement unpopular reforms it has already agreed, it said on Sunday.
chairperson