William Morgan Butler was a lawyer and legislator for the State of Massachusetts, and a United States Senator.

The president of the Massachusetts Senate is the presiding officer. Unlike the United States Congress, in which the vice president of the United States is the ex officio president of the United States Senate, in Massachusetts, the president of the Senate is elected from and by the senators. The president, therefore, typically comes from the majority party, and the president is then the de facto leader of that party.