Who is Sheriff James G. Clark from A Testament of Hope: The Essential Writings and Speeches of Martin Luther King, Jr and what is their importance?

Sheriff James G. Clark, of Selma, Dallas, Alabama, is described as a shrewd, avid segregationist, who fought giving the right of the ballot to the Negro. He refused to use brutality in front of the television cameras, but when the marchers left his jurisdiction and went into state jurisdiction, they were beaten unmercifully in front of the cameras for the nation to see.