In Gottfried’s Tristan, this mischievous knight was enamored with Isolde. Skilled in playing the rote (a type of stringed instrument), he traveled to Mark’s court and entertained Mark with his music. Mark was led to make a rash promise to grant Gandin anything he wished, and Gandin chose Isolde herself. Mark had little choice but to lete Gandin carry her off.
Tristan followed the pair and tricked Gandin – by playing his harp – into giving Isolde back.
Gottfried may have taken the name from Wolfram’s character. In the Prose Tristan, this abduction is replaced with one by Palamedes.
Source
Tristan | Gottfried von Strassburg, early 13th century