who was the other robin in batman vs robin

The “other Robin” in Batman vs. Robin is Damian Wayne , Batman’s son. The movie centers on the conflict between Bruce Wayne and Damian after Damian is already operating as Robin.

In case you meant a different Batman title:

• Batman & Robin is the 1997 live-action film with Dick Grayson as Robin.
• Batman vs. Robin / Batman v. Robin refers to stories focused on Damian Wayne as Robin.

TL;DR: It’s Damian Wayne.