Tironium

Tironium is a substance from the Beast Wars portion of the Generation 1 continuity family.

Tironium is an extremely tough, ultra-light metal.

Fiction

Beast Wars cartoon

Upon observing Terrorsaur after he absorbed unstable energon into his superstructure from the flying mountain, Rattrap commented that, with his newfound power, the Predacon looked like he could "eat tironium". Power Surge

Transformers Animated

Megatron's two swords are made of tironium, an ultra-light metal developed by Sumdac Systems. AllSpark Almanac