Heatran is a reddish-brown, quadrupedal Pokémon. It is dotted with orange and gray spots, and it has metal bangles locked on its legs. Its four claws on each of its feet are in a cross formation. Heatran has a gray underside, and its face is covered by an iron mask, with red-orange eyes uncovered. Its eyes seem to remain open even when it is asleep. Whenever it is seen with its mouth open, an orange glow emanates from inside it. Boiling magma-like blood circulates through its body. While its body is rugged steel, certain parts of it are partially melted, due to Heatran's own intense body heat.
Heatran is a fierce guardian. Without the power of the Magma Stone, Heatran would rampage and cause the volcanic crater where it dwells to erupt. Heatran's claws allow it to dig deep into walls, and its feet allow it to stick to a surface, so it can hang and climb from walls and ceilings. According to legends, Heatran was said to have been created from the magma hidden beneath Mount Coronet. The body of Heatran is said to hold many unsolved mysteries. Heatran has the ability to form a shield around itself in order to protect itself from harm.
In Pokémon Adventures, Heatran is referred to as the "Lord of Stark Mountain." It first appeared in Clobbering Claydol, where Buck sought to protect it from Team Galactic by taking the Magma Stone with him. However, him doing this caused Heatran to be unsealed, allowing Charon to catch it for his own use. Throughout the Platinum chapter, Charon used Heatran in his battles against Sinnoh's other Legendary Pokémon, until he was finally defeated at the end of the chapter. Following Charon's arrest, Buck agreed to take Heatran back to Stark Mountain.
In the Japanese version of Pokémon X and Y, two women in Jaune Plaza mimic the sounds of Pokémon. One mimics the sound of a Heatran, while the other compliments her. However, this is mistranslated in the English version to say that there is a Lava Dome Pokémon in Jaune Plaza.
Heatran is the only Pokémon introduced before Hidden Abilities that cannot be obtained with its Hidden Ability in any game without an Ability Patch.
Heatran is the only Legendary Pokémon to not be related to another Legendary or Mythical Pokémon through a legendary grouping (such as a duo or trio), evolutionary chain, or in-game lore.
Heatran may be based on volcanic remains. Its Steel typing may reference how the Earth's inner core is made of solid metal under immense pressure. It may be also based on a personification of magma. In the ancient mythologies of most cultures, the eruptions of volcanoes were explained by the presence of a fire monster living within it, often a dragon.
Heatran may be derived from heat transfer. Its Japanese name may involve ドラゴン dragon.