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. Because of its intense body heat, certain parts of its body are melted slightly out of shape. Boiling blood, like magma, circulates through its body. While its body is rugged steel, it melts partly due to Heatran's own 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 JNS01, Saturncaught a Heatran to be used in Team Galactic's plan to bring back Cyrus, using it and a Flame Plate to power an energy cannon. However, in JNS02, Saturn accidentally overloaded the cannon, causing it to backfire and send Heatran on a rampage when its Flash Fire Ability overloaded, melting its Dusk Ball and escaping. Its rampage was eventually stopped in JNS04.
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 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 generic volcano monster: 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.