Yacatecuhtli: [Aztec Empire/Mexico] The Aztec god of travelling merchants.
Yankee Doodle Pigeon: [USA] Hanna & Barbera's secret agent pigeon.
Yellow Claw, The: [USA] The Chinese Would-be World conqueror from the Atlas/Marvel Universe (616 continuity).
Yukio: [USA] Wild One, assassin/adventurer from Marvel Universe 616.
Youngblood: [USA] Organization from both Rob Liefeld's part of the original Image Universe and his revised universe.
Yusef: [USA] Character from Broadway Comics.