Take context from the input text and decide on the accurate relationship between 'Syriza' and 'Alexis Tsipras' from the options provided.
Options: legal form, business division, owner of, chairperson

Prime minister Alexis Tsipras is also battling an internal revolt among his Syriza party over the recessionary measures he was forced to submit to in a July 13 agreement.
chairperson