Galeem (キーラ, Kiira) is one of the two main antagonists of Super Smash Bros. Ultimate's Adventure Mode: World of Light. He is described as "Lord of Light" and the "ultimate enemy" in the World of Light. His goal is to recreate the universe in his own image. His dark counterpart is named Dharkon.
Prior to the events of the mode, Galeem attacks the fighters, commanding an army of Master Hands. He uses his light attack to destroy and imprison all fighters with the sole exception of Kirby after his Master Hands disintegrate and their energy fuses with him, in addition to turning every non-playable character into a spirit. His attack goes on to engulf the entire universe in a burst of light, leaving what is left of the world a barren wasteland inhabited by hostile spirits and puppet fighters cloned from the fighters imprisoned by him. After Galeem's first defeat, Dharkon appears along with his army of Crazy Hands, driving Galeem away. Galeem later returns when Dharkon is defeated and flees into a dark portal, with Galeem in pursuit.
In the final world, Galeem wages war with Dharkon, while also seeking to destroy the fighters. If only Dharkon is defeated, Galeem destroys Dharkon's army and strikes him down, killing him by engulfing the world in light, resulting in one of two bad endings. The true ending can be obtained by defeating both Galeem and Dharkon. Both Galeem and Dharkon are finally defeated by the fighters, sinking into the ocean and exploding thereafter.
Galeem's core is the only place it can be damaged. He can be stunned, which drops the core on the stage for several seconds. Once his health drops below half, Galeem's core will constantly emit a bright shine.
Note that many attacks' characteristics, such as number of projectiles fired, vary depending on both Galeem's health and which battle it is. Also, certain attacks are never used in certain battles.
During the final battle with Galeem and Dharkon, both bosses will deliberately target the player. However, they remain mortal enemies as their attacks can harm each other but only the player can deal the final blow.