Adamantium is a fictional metal alloy appearing in American comic books published by Marvel Comics. It is best known as the substance bonded to the character Wolverine's skeleton and claws. Adamantium was created by writer Roy Thomas and artists Barry Windsor-Smith and Syd Shores in Marvel Comics' Avengers #66 (July 1969), which presents the substance as part of the character Ultron's outer shell.^[1] In the stories where it appears, the defining quality of adamantium is its practical indestructibility.

The word is a pseudo-Latin neologism (real Latin: adamans, from original Greek ἀδάμας [=indomitable]; adamantem [Latin accusative]) based on the English noun and adjective adamant (and the derived adjective adamantine) added to the neo-Latin suffix "-ium." The adjective adamant has long been used to refer to the property of impregnable, diamondlike hardness, or to describe a very firm/resolute position (e.g. He adamantly refused to leave). The noun adamant describes any impenetrably or unyieldingly hard substance and, formerly, a legendary stone/rock or mineral of impenetrable hardness and with many other properties, often identified with diamond or lodestone.^[2] Adamant and the literary form adamantine occur in works such as The Faerie Queene, Paradise Lost, Gulliver's Travels, The Adventures of Tom Sawyer, The Lord of the Rings, and the film Forbidden Planet (as "adamantine steel"), all of which predate the use of adamantium in Marvel's comics.

According to the comic books, the components of the alloy are kept in separate batches—typically in blocks of resin—before molding. Adamantium is prepared by melting the blocks together, mixing the components while the resin evaporates. The alloy must then be cast within eight minutes. Marvel Comics' adamantium has an extremely stable molecular structure that prevents it from being further molded even if the temperature is high enough to keep it in its liquefied form. In its solid form, it is described as a dark, shiny gray, like high-grade steel or titanium.^[3] It is almost impossible to destroy or fracture in this state, and when molded to a sharp edge, it can penetrate most lesser materials with minimal force.^[4]

The Marvel Comics character Wolverine discovers an adamantium-laced skull in the character Apocalypse's laboratory and says it seems to have been there for eons.^[5]

Adamantium appears in various Marvel Comics publications and licensed products, where it is found in:

In the Marvel Comics Ultimate Marvel imprint, adamantium is highly durable and can shield a person's mind from telepathic probing or attacks. It is a component of the claws and skeleton of Ultimate Wolverine and of the Ultimate Lady Deathstrike character. This version of adamantium is not unbreakable. In Ultimates #5, the Hulk breaks a needle made of adamantium. In Ultimate X-Men #11 (December 2001), an adamantium cage is damaged by a bomb. In Ultimate X-Men #12 (January 2002), one of Sabretooth's four adamantium claws is broken.^[12]