Rashi: Their savior, who breaches the fence of thorns to straighten the path in front of them.

Radak citing his father: This refers to Tzidkiyah, when he left from between the walls. They breached the wall in front of him, like it says "ba'Kir Yachteru Lehotzi Vo" (Yechezkel 12:12).

Radak citing a Midrash: This is Eliyahu.

Malbim: It is a king of Yehudah who breached the fences of our creed and served idolatry. Immediately the nation was drawn after him to do like him, like in the days of Achaz and Menasheh. When a virtuous king rose after him, like Chizkiyah after Achaz and the yoke of Shamayim after Menasheh [and Amon], that they began to serve Hashem, also the entire nation did so. This shows that Emunah is not rooted in their hearts. They are drawn after their leader ? to follow Hashem or Azazel (idolatry). Our verse teaches that when a king arose who breached fences, annulled the creed and razed its walls, [also the nation] breached and transgressed. Afterwards there was a breach in the gate fixed to go in it, and they left the creed.

Radak: This is Tzidkiyah, who fled in front of his army, and they fled after him.

Radak citing a Midrash: This is Tzemach (Mashi'ach) ben David.

Malbim: A Melech Tzadik who rules. Then, they are drawn after Hashem.

Radak: Before, Hashem was at their head. The Shechinah departed, and they were exiled.

Malbim: Refer to 2:12:2:3.