Tony Stark's new element

In 2010 in Earth-199999, Tony Stark synthesized a new element to replace the palladium that was slowly poisoning him from within the arc reactor in his chest.

This synthesis was necessary because no other known element would suitably power the arc reactor except for palladium, and there was also no long-term solution to counter the palladium poisoning. Stark had essentially given himself up for dead with days to live when Nick Fury of S.H.I.E.L.D. provided him with a collection of documents belonging to his father, Howard Stark. Tony watched a film reel therein in which Howard told him that the 1974 Stark Expo was "the key to the future," and that while the technology of his own time was limited, he was confident that Tony would figure it out. Tony examined the topography of the expo's grounds, and after disregarding various superfluities of the landscape, found that it resembled an atom of a previously undiscovered element.

Essentially, Howard Stark had designed the arc reactor to run on palladium because he was unable to create the element he had discovered with what he had available to him at the time. J.A.R.V.I.S. declared that it would be impossible to synthesize, but Tony quickly proved him wrong, successfully synthesizing it within the day. Installing it in his arc reactor, Stark declared that it tasted "like coconut and metal." The installation went off without a hitch, and the new element proved a perfectly suitable replacement for palladium. Furthermore, S.H.I.E.L.D. found the element useful in their experiments with the Tesseract as part of Project P.E.G.A.S.U.S., using it to stabilize the Tesseract's power levels. Stark wanted to call the element badassium, but "encountered several bureaucratic obstacles," in Fury's words. As a result, the element remains officially unnamed.