Blue-Eyes White Dragon

The Blue-Eyes White Dragon was the most powerful card in Kaiba's deck until he obtained Obelisk the Tormentor. It could combine to make the Blue-Eyes Ultimate Dragon.
There were only four Blue-Eyes in existence - Kaiba obtained three, and then destroyed Solomon Muto's copy.
Pegasus once used Toon World on the Blue-Eyes White Dragon, creating his own Blue-Eyes Toon Dragon.
Kaiba has a jet shaped like a Blue-Eyes White Dragon.