Allegedly the first being to free itself from the timestream, Alioth grew in power, becoming the supreme time being over all realities from the dawn of life on Earth to the edge of Kang the Conqueror’s dominion. A temporal barrier blocked Alioth from entering Kang’s realm, Chronopolis, and conquering all time periods.
After Kang was rendered comatose saving the Terminatrix (Ravonna Renslayer), she took over Kang’s empire. Exploring an anomaly at the edge of Kang’s domain, she encountered the time barrier; curious, she blasted it to learn what it hid, apparently summoning or releasing Alioth. Terminatrix fled, but Alioth followed, assaulting Chronopolis city. Aided by her own potential future self Revelation, Terminatrix revived Kang, but Alioth absorbed the Council of Cross-Time Kangs.
Narrowly escaping absorption, Kang and Terminatrix enlisted the Avengers to enter Alioth’s substance within the Council’s chambers and activate Kang’s Chrono Key, which transformed into the monolithic warrior Tempus. Absorbing the Council members’ energies and then Alioth’s own power, Tempus grew gigantic, eventually reaching reality-wide proportions and spreading across the timestream, creating the time barrier between Alioth’s realm and Chronopolis.
Tempus thus held Alioth at bay, just as he always had, except for a brief ripple in time; Kang later claimed he arranged Alioth’s release to eliminate the Council. Kang subsequently weakened Tempus slightly, allowing Alioth to break into the Time Variance Authority’s realm, throwing them into turmoil.
A trans-temporal entity, Alioth exists across divergent realities as an enormous cloud destroying all it touches, causing massive temporal disturbance and devastation across entire dimensions. It can extend pseudopodia to attack focal beings or locations. It grows in size and power by absorbing time travelers’ bodies into its mass. Once it occupies a time period, it spreads out to engulf the adjacent realities.
Alioth also negates temporal energy, preventing travel through it to a time before it exists. Attempts to travel through Alioth usually result in the traveler’s absorption.