Rabbi Isaac ben Asher HaLevi or Riba (ריב"א) is the earliest known Tosafist, son-in-law of Eliakim ben Meshullam and pupil of Rashi.
They are frequently quoted without the name of their author.
Isaac ben Asher also wrote a commentary on the Pentateuch, which is no longer extant.
It is cited in the Minchat Yehudah, and Jacob Tam made use of it in his Sefer ha-Yashar (p. 282).
He was also the teacher of Isaac ben Mordecai of Regensburg and Ephraim ben Isaac of Regensburg.