The successful isolation and characterization of Th@C₈₂, U@C₈₂, U@C₇₄ have shown that actinide fullerenes have unique properties which are previously unknown to the endohedral fullerene world. Now, with the further exploration of actinide endohedral fullerenes based on U and Th, we found these endohedral fullerenes are unique for not only fullerene chemistry but also to actinide chemistry. U@C₈₀ and U@C₇₆ have been found to process Non-IPR cages, which are rare cases for the mono metallic endohedral fullerenes. Th@C₈₆ and U@C₈₆, on the other hand were found to share the same IPR cages, where have never been reported before. The crystallographic and computational studies of U₂C@I_h-C₈₀ reveal reveals a cage-stabilized, carbide-bridged, bent UCU cluster with unpreced­entedly short uranium-carbon distances (2.03 Å) of genuine U=C double-bond character. The isolation of U₂C@C₈₀ gives an unprecedented look into a long sought after but heretofore unknown U=C bond which lacks heteroatom support, allowing for detailed structural and electronic insights.