Ultron Sigma is the merged form of Ultron and Sigma that appears as an antagonist in Marvel vs. Capcom: Infinite. His "voice" is that of both Ultron and Sigma's voices overlapping each other, owing to his being fused from the two characters.
In the demo, Thor, alongside Rad Spencer, challenges Ultron Sigma for the throne of Asgard (renamed Xgard under Ultron Sigma's rule), with Ultron Sigma declaring arrogantly that their will is law and thus they will destroy them. Regardless of whether the player wins or loses, however, the demo will end the same way once Ultron Sigma's health is whittled down to a third: Ultron Sigma will disable Spencer and Thor with a chest blast and a beam saber slash, respectively, and then decries them as pitiful before asking if they even realize how powerless they truly were. He then steps on Thor's hand just as he reached for Mjolnir, and declared that he is not to weep for the Asgardians due to their achieving perfection under his rule. He then cruelly tells Thor that he'll soon "be their prince once more" before charging up an energy blast on his arm to transform him into a Xgardian. Before he could land the final blow, however, Ultron Sigma was shot in the back. Unphased by the gunshot, Ultron Sigma, realizing that Chris Redfield was behind him and shot him, calmly asks him if the commander had something to add in terms of great insight. Chris, however, merely tells him that he's going down. Ultron Sigma expresses some mock-disappointment in that all he had to offer was a "banal cliché" before declaring it to be fitting as final words from him. Ultron Sigma then levitates up and proceeds to charge up an attack above him before firing at Chris Redfield. However, Captain America deflects the blast with his shield, while Strider Hiryu retrieves Thor and teleports behind, with Ultron Sigma noticing just as it happens. The heroes then escape via Doctor Strange's portal, although Ultron Sigma nonetheless is glad over the overall turn of events despite losing his quarry.