In the context of the input sentence, determine the relationship between 'Syriza' and 'Alexis Tsipras'.
Options: owned by, currency, chairperson, headquarters location

Prime Minister Alexis Tsipras resigned last week after his acceptance of an 86 billion euro ($96 billion) rescue package for Greece's stricken economy triggered a major rebellion within his radical left Syriza party.
chairperson