Take context from the input text and decide on the accurate relationship between 'Syriza' and 'Alexis Tsipras' from the options provided.
Options: chief executive officer, employer, chairperson, creator

The latest news from Greece, where Prime Minister Alexis Tsipras contained a rebellion in his left-wing Syriza party to win a parliamentary vote, was seen as another positive for European markets.
chairperson