True Hero? A Bad Question
Mike B.

All of the people listed in the question were essential to the destruction of the ring. If anyone of them had messed up (not acted as they did in the story), it would have ended in disaster. Here is why each one is essential:

Frodo -- he accepted the quest and carried the ring. If he hadn't, Rivendell would have eventually been invaded and the ring recovered.

Sam -- he prevented the enemy from getting the ring after Frodo was stung by Shelob. If he hadn't taken the ring from Frodo, Sauron would have gotten the ring back and won.

Gandalf -- he discovered that the ring that Bilbo found was the One Ring. If he hadn't, Frodo would have been murdered by a black rider one night and they would have gotten the ring. He also guided them from Rivendell to the end of Moria.

Aragorn -- he prevented the black riders from getting the ring back in Bree by getting Frodo to sleep somewhere else. He also guided the hobbits from Bree to Rivendell.

Gollum -- he prevented Frodo from claiming the ring himself by biting off Frodo's finger. If he hadn't, Frodo would have been killed by Sauron and would have lost the ring to him.

Boromir -- he revealed to Frodo that the ring was a temptation to everyone in the fellowship. If they would have gotten closer to Mordor, the ring might have corrupted someone more important like Aragorn, Gimli, or one of the other hobbits. He also caused the splitting of the fellowship and if this hadn't happened, Rohan would have lost to Isengard (because Gandalf, Aragorn, Gimli, and Legolas helped Rohan win).

Bilbo -- he found the ring before any orc could and therefore prevented Sauron from recovering it.

All of these characters were heros and equally important along with certain orcs like the ones who kill each other in the tower above Cirith Ungol.