Atlas Flame is an enormous dragon with the usual characteristics; having a massive body, a pair of wings that allowed him to fly, four limbs with claws, and a tail. Unlike most dragons, Atlas Flame's body is covered in flames instead of scales which gives him the appearance of a burning skeleton.
There is little to know about Atlas Flame's personality. However, unlike the dragons who considered humans as food, he actually cared about introducing himself to the Fairy Tail Guild that faced him, and told them they were going to experience "the flames of hell" before he fought them. He is also known for having a strong will and is respectful to those he consider dear friends, as when Atlas Flame found out that Natsu was the foster son of his dear friend Igneel, the dragon broke free from his master's control and fought alongside Natsu out of respect for Igneel.
At some point in the past, Atlas Flame constantly fought against the Flame Dragon King, Igneel. During those battles, Igneel would be the victor and consume the fire dragon's flame. Atlas Flame would eventually forge a deep respect for Igneel and consider him a dear friend. After living his natural life and his return to the past, Atlas Flame created the Sun Village and became its guardian: The Eternal Flame. He eventually died, but a portion of his spirit remained in the Eternal Flame, but was frozen solid by the Tartarus member called Silver, who mistook him for a demon, by using his ice.
Grand Magic Games
Atlas Flame, alongside the other dragons, appears out of the Eclipse Gate that managed to get through the gate, before it was closed by Lucy Heartfilia and Yukino Aguria. When Future Rouge arrived to the Eclipse Gate, it is revealed that Atlas Flame and the other dragons are controlled by him via his Dragon Supremacy Magic. As his master announces the end of humanity and the start of the Dragon Era, Atlas Flames follows his master's order - to kill all the mages in Crocus. He then arrives to the location where Fairy Tail is. Before he began to fight Fairy Tail, he tells them his name and that he tells them they will taste the "Flames of Hell".
Atlas soon fought against the Thunder God Tribe only for Natsu to appear on his back and consume his flames. Annoyed that a mere "human" would try to devour him, he attempted to shake him off but in doing so he is reminded of his past battles with Igneel. Stopping his actions, Atlas questions Natsu on his connection to Igneel as the dragon slayer is shocked that Atlas knows of his foster father. Atlas reveals Igneel is an old friend of his as Natsu happily tells him that Igneel is his father.