William I "the Elder" of Hesse-Rotenburg (15 May 1648, in Kassel – 20 November 1725, in Langenschwalbach) was from 1683 until his death Landgrave of Hesse-Rotenburg.
He was a son of Ernest I of Hesse-Rotenburg-Rheinfels and his wife, Countess Maria Eleonore of Solms-Lich.
William was nicknamed the Elder to distinguish him from his nephew, William of Hesse-Wanfried.