O adamantium não é exclusivo do Wolverine. O shell do Ultron é feito do mesmo material.
The first use of the term adamantium in Marvel Comics was in Avengers #66 (July 1969) as part of Ultron's outer shell. The word is a pseudo-Latin coinage (real Latin: adamans, adamantem [accusative]) based on the English noun and adjective adamant (and the derived adverb adamantly). The adjective has long been used to refer to the embodiment of impregnable, diamondlike hardness, or to describe a very firm/resolute position (i.e. He adamantly refused to leave). The noun adamant has long been used to designate 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.
Adamant and the literary form adamantine occur in works such as the Aeneid, The Faerie Queene, Paradise Lost, Gulliver's Travels, The Adventures of Tom Sawyer, The Lord of the Rings, and the film Forbidden Planet, all of which predate the use of adamantium in Marvel's comics. Adamantine is also the metal used by Hephaestus to construct chains to hold Prometheus in the ancient greek play Prometheus Bound.
A ideia está relacionada com Unobtainium , um material usado em muitas ficções científicas, que tem propriedades que o autor precisa mover a história.