Legend of Vighneshwar Ashtavinayak
A king called Abhinandan one day decided to become the King of Heaven. To achieve this goal he started a Yagya, a sacrifice. When Indra the King of Heaven heard this he decided to create obstacles in the king's path. He summoned Kalapurush and asked him to destroy King Abhinandan's Yagya. After doing so Kalapurush acquired the name Vighnasura, the creator of obstacles.
Vighnasura then went on a rampage and destroyed all Vedic practices on earth. The gods realised that they had to destroy this destructive force and they turned to Gajanan for help, who in those days was at the ashram of Sage Parashar.
Gajanan took birth as the son of Parshwaputra and his wife Deepvatsala. This son then fought valiantly with Vighnasura, who had to except defeat. He abdicated himself to the Lord and asked to be blessed. Ganesh said that he would be let him go, but made him promise that he would never enter any place where Lord Ganesh was being worshipped. Vighnasura accepted this on condition that Lord Ganesh be known by his name.
So Lord Ganesh came to be known as Vighneshwar or Vighnaharta.
Ozhar it is believed is where Lord Ganesh resided as Vigneshwar.