Moon Lord

The Lunar Boss the final boss after Duke Fishron/Ocram that Redigit has hinted will be adding in a future Terraria update. People originally thought the boss would be the moon itself, however Red stated this was not the case.

It is also the name of the final song in the Terraria soundtrack volume 2. The lunar boss is also the boss that when you kill it, it will unlock the summoner for the wall of steel, another wall of flesh boss.