The door gods posted on the door usually refer to the military generals Qin Shubao and Yuchi Jingde
It is said that Emperor Taizong of the Tang Dynasty was not in good health and always felt that there were noises in the palace and was very scared. So Taizong told all the ministers about the situation, and Qin Shubao reported: "In my life, I killed people as if they were withering, and accumulated corpses as if they were gathering ants. Why should I be afraid? I am willing to serve with respectful military uniforms." Taizong approved the report, and asked the two to stand at night. On both sides of the palace gate, the night was indeed peaceful.
After Taizong commended the two of them, he felt that it was really hard for them to guard the palace gate all night, so he ordered a painter to draw a portrait of the two of them. As usual, it was hung on the two palace doors, and it was calmed down from then on. It was not until the Yuan Dynasty that people followed this practice and worshiped the two as door gods.
Extended information
According to historical records, the activity of "sacrifice to the gate" had already appeared in the Zhou Dynasty, and it was an extremely important ceremony. Among the legends of door gods, the legends of Shen Tu and Yu Lei have long been circulated among the people. They can be found in classics such as "The Classic of Mountains and Seas", "General Meanings of Customs", "Revisiting the Collection of Weishu", and "The Encyclopedia of Searching Gods from the Origins of Three Religions". record.
The birthday of the door god is the 15th day of the first lunar month. During the New Year, people often worship the door god and post it at the door (from the perspective of the person entering the door, it is posted on both sides of the door. In the painting, the door god is Facing each other's faces is considered the correct traditional way of pasting, while facing each other is a folk custom of "pasting the wrong door god").
Some famous places where traditional woodblock prints are produced are also famous for printing door god prints, such as Yangliuqing, Weifang and Taohuawu. The paintings of door gods are also colorful, some wear tiger helmets, and some wear robes. The New Year paintings are also decorated with festive patterns such as jue deer, bats, BMWs, bottle saddles, etc. to pray for good luck.
The custom of putting a door god on the door of your home during the Spring Festival has been passed down for thousands of years.
Reference material - Baidu Encyclopedia Door God