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. Heatran is the only known Pokémon that learns Magma Storm.
In Pokémon Adventures, Heatran is referred to as the "Lord of Stark Mountain." Heatran first appears in the Platinum chapter after Buck goes to Stark Mountain to try to prevent Team Galactic from getting to it first. However, after Buck removes the Magma Stone that sealed Heatran, Charon captures it and uses it to attack Buck. Charon takes Heatran to Eterna City to battle Regigigas, who had joined Diamond's team as Reg. The battle is interrupted when Charon decides to follow the rampaging Giratina back to the Distortion World. There, the battle between Heatran and Reg resumes, with the lake guardians assisting Reg. At the end of the arc, Buck announces that he would escort Heatran back to Stark Mountain. Cheryl and Mira agree to help. It first appeared in Clobbering Claydol.
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 has the lowest number of Egg cycles of all Legendary Pokémon, with 10.
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.