Of all of the many monsters in Dungeons and Dragons, none are more feared, resented, and rare as the Tarrasque. Its immense power makes it the perfect final boss, but more frequently than that, it is something that the players must either avoid or prevent from waking at all costs. This creature has changed significantly over the course of several editions, but remains one of the top dogs of whatever book it is in, whether it appears in Forgotten Realms or Eberron.
For the uninitiated, the Tarrasque is a massive, quadrupedal beast with a reputation for being the single most powerful creature to live on the material plane. Nothing else comes close to this beast's ferocity and tenacity, but it has several weaknesses as well. The Tarrasque was first introduced in Dungeons and Dragons' first edition Monster Manual II. It was here that its position as an essentially unkillable titan was cemented thanks to its numerous defensive abilities and extremely high damage output capabilities. Since then, the Tarrasque has appeared in every incarnation of D&D including 5e, although the beast is admittedly toned down quite a bit in its most recent incarnation.
One can't speak of the Tarrasque without first describing its monstrous size and appearance. The Tarrasque is said to stand 50 feet tall, and with its massive tail, measures about 70 feet long. The beast is covered in a reflective, incredibly tough carapace, and riveted with spikes the size of large buildings. Its armored hide provides it with many defensive capabilities, while its gaping maw contributes to its destructive potential. Destructive is indeed the best word to describe the Tarrasque, for it is not evil in any way, it just simply lacks all sense of morality, instead depending purely on primal instincts.
Historically, the Tarrasque has incredibly high armor class, the ability to reflect spells, and perhaps most notably, nearly limitless regenerative abilities. Interestingly enough, however, this last and most recognizable of traits is mysteriously absent now. In prior editions, the Tarrasque was capable of regenerating from literally anything. In 3.5e, it was impossible to deal lethal damage to this creature, even through the use of powerful spells like the wizard's disintegrate spell. Even killing this creature is not permanent, requiring a wish spell to seal the deal. It is somewhat strange that this ability was removed from the Tarrasque of fifth edition, since it played an important role in the creature's undying reputation.
The Tarrasque's purpose is literally to eat the world. Whenever it wakes from its slumber, the Tarrasque wanders the material plane, eating anything that crosses its path: Mountains, kingdoms, people, and monsters, none are safe from its endless hunger. In D&D 3.5e, the Tarrasque could swallow whole anything huge or smaller which it hits with its bite, meaning even things like some adult dragons or tyrannosaurus rexes could simply be devoured. Again, 5e sees this ability dumbed down a bit, reducing the size maximum to large. Similarly, the Tarrasque's natural weapons used to ignore all resistances and damage reduction, but no longer does.
The only reason the material plane hasn't been eaten yet is because the only thing that rivals the Tarrasque's need for hunger is its need for sleep. The beast sleeps for long periods of time, only waking when something disturbs its slumber, or when the vast amounts of food it has eaten stops providing enough energy. Dungeon masters that want to use the Tarrasque should do so with utmost care, as this creature is more than capable of completely wiping a party. Players on the other hand should avoid encountering this beast at all costs, as even at level 20, this foe is dangerous. The ultimate goal for Dungeons & Dragons players should be to stop it from waking in the first place.