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

?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