Analyze the relationship between 'Syriza' and 'Alexis Tsipras' within the context of the input sentence.
Options: chief executive officer, subsidiary, chairperson, owner of

?Equity markets largely in the red... coming down off yesterday's heady reaction to news of a Greek deal, as Alexis Tsipras returns to a revolution within his Syriza party," said Augustin Eden, research analyst at trading firm Accendo Markets.
chairperson