What saint persecuted Christians?

A great many Christian saints persecuted Christians who held beliefs other than their own. It was a characteristic of the early Church that dissent was labelled heresy, and heretics deserved nothing less than torture and execution. Those who succeeded in furthering the objectives of the dominant Church were rewarded with the nomenclature of 'Saint'.

Roman Catholic AnswerI believe you may be asking about St. Paul, who before his conversion to the faith persecuted the Christians unmercifully. His Jewish name was Saul, and his persecution of the Christians is outlined in the Acts of the Apostles.