Tlahuizcalpantecuhtli (also Tlahuixcalpantecuhtli) is the Lord of the House of the Dawn, Venus as the Morning Star. Tlahuixcalpantecuhtli is a manifestion of Quetzalcoatl. His twin is Xolotl, Venus as the Evening Star.
Tlahuizcalpantecuhtli is a god of war.
In Teotihuacan Tlahuixcalpantecuhtli attacked Tonatiuh, the newly created Sun, by throwing an atl-atl dart at him. Tlahuixcalpantecuhtli missed. Tonatiuh threw a dart back, piercing Tlahuixcalpantecuhtli through the head. This transformed Tlahuixcalpantecuhtli into Itztlacoliuhqui, god of stone and coldness.
In the tonalpohualli, Tlahuizcalpantecuhtli is the Lord of the Day for days with number 12 (mahtlactli-omome in Nahuatl).