The Cave of Wonders Guardian resembles a massive tiger's head. In Aladdin, its eyes are shown to be the two halves of a scarab talisman used to find it. It is comprised entirely of sand, though it appears to be dark blue because the area around the Cave of Wonders is always seen at night. Its mouth, which is lined with sharp teeth, houses a staircase into the cave, and the lights from within the cave give off a dim glow visible from the Guardian’s throat.
In Kingdom Hearts, Sora, Aladdin, Donald, and Goofy fight it after it's taken over by the Heartless and tries to destroy them. Once they destroy the dark power's source, which is located in his eyes (reached by climbing up its neck or by leaping onto its face when it's buried in the dirt), the guardian returns to being an entrance to the Cave of Wonders, and continues to be so throughout the series.
In Kingdom Hearts coded, Jafar places a spell on the guardian, and Sora must complete a system sector to enter the Cave of Wonders.
The Cave of Wonders guardian originates from the movie Aladdin. At the start of the movie, Jafar attempted to use a bandit to get inside, but is unable to as he needs the chosen one. However Jafar then used Aladdin to go into the Cave of Wonders to get him the Genie's lamp.