The Red Dragon is a form of the Biblical Satan, otherwise known as Lucifer, the former Seraphim that rebelled against the Creator and became evil in Christianity and Hebrew religions.
His alias, the Red Dragon, was described in the Bible to have seven heads, ten horns, seven crowns, and a massive tail that knocks one-third of the stars out of the sky.
The Red Dragon is mentioned to have other names like the Serpent of Old and the Devil. It is said in the Bible that Satan will take the form of the Red Dragon and will along with the Antichrist, the False Prophet, and the Beast, deceive most of Humanity. After that the Red Dragon will be set free upon the world in which he will rule alongside demons for three long years. After that God will cast the Red Dragon, demons, and other dammed evil souls into Lake of Fire, thus finally destroying the evil of Satan forever.
The depiction of Satan as the Red Dragon was likely to symbolize him as the supernatural ruler of the Roman Empire, which Christianity was heavily affected by at that time of history. The image of the Red Dragon later influenced cultural and religious perceptions in medieval Europe that dragons were generally of an evil nature.