Long ago the Kymellians destroyed their homeworld attempting to generate energy via a matter/anti-matter conversion, causing a cataclysmic chain reaction. When Aelfyre "Whitey" Whitemane, a Kymellian studying humanity by tapping into mankind's transmissions and computer network, learned a human scientist, Dr. James Power, was about to test the same process on Earth, he felt he had to intervene in spite of his race's non-interference laws. He sent a signal to his people requesting permission, but it was intercepted by the warlike Snarks (slang for the race translated to English as Z^nrx or Sn^rx), who sent ships to steal the process. They shot down Whitey's Smartship Friday, though not before he managed to remotely wipe Power's computers, leaving James the only person who knew the process.
The aerial battle was witnessed from the Powers' beachfront house by Katie, James' youngest daughter, but the rest of the family believed her sighting to be shooting stars. Hoping for more stellar displays, the Power children-Alex, Julie, Jack and Katie-slept out on the porch; that night Katie spotted Friday floating in the sea, and they went to have a closer look. Jack and Julie returned home to get their parents, but as they neared the house they saw the Snarks capturing James and Margaret Power. The children tried to stop the aliens, but were about to be killed when Whitey intervened. Though he saved the kids, Whitey was badly wounded, and the Snarks escaped with the two adults. Before he expired, Whitey transferred his ability to control aspects of energy, mass, acceleration, and gravity to the children.
At Jack's suggestion they each chose super-hero names: Alex became Gee, able to control gravity; as Lightspeed, Julie could fly and left a trail of rainbow light; Katie became Energizer, able to convert physical objects to energy, then absorb and discharge it as destructive bolts; while Jack's ability to become cloud-like and later tiny and super-dense made him Mass Master (failing to appreciate that, perhaps due to human/Kymellian variation, he altered his density and volume, not his mass). Friday provided them with unstable molecule costumes, and they dubbed themselves Power Pack. They saved the world from annihilation by destroying their father's prototype conversion device, but his boss Carmody recognized them, assuming them to be mutants. They rescued their parents from the Snarks, whose interrogation methods had destroyed portions of their father's memories, leaving him unable to recreate his process. Carmody reported them to the government, but his anti-mutant obsession and attempts to harm them backfired; a mutant detector marked them as human, and after Carmody endangered the children, Dr. Power quit, taking a job in New York.
Within days of arriving in the Big Apple, Power Pack encountered Spider-Man, Cloak and Dagger, Dragon-Man, and Marrina, as well as enduring the travails of starting new schools and making new friends. They encountered the Morlocks and the X-Men in the sewers, being briefly kidnapped and brainwashed to replace Annalee's dead children. Carmody returned, using a Project: PEGASUS surplus battlesuit to become the Bogeyman, but was warned off by the children's new friends, the Asgardian Warriors Three. Shortly after this, Franklin Richards, son of Mister Fantastic and the Invisible Woman, began to see Power Pack in prophetic dreams, while on Snarkworld Whitey's cousin Kofi learned that High Snark Jakal was heading to Earth to steal the children's abilities, hoping to use them to become the next Emperor. Kofi raced to warn them, but was shot down, crashing near the Statue of Liberty. Franklin encountered the Power children in Central Park and led them to the injured Kymellian, but they were ambushed by Jakal. Assisted by Franklin and Kofi, they defeated him, and Franklin joined Power Pack as Tattletale.
Soon after they met the Beyonder during his super-hero phase, and fought Kurse after he hospitalized their mother, later assisting Thor and Beta Ray Bill in defeating the dark elf. Next they stopped demons hoping to gain power to overthrow their ruler Magik (Illyana Rasputin), from sacrificing Katie, while Magik's teammate Mirage used her Valkyrie powers to keep Death from claiming Margaret Power. Jakal's mother Maraud kidnapped the Power children and Kofi, taking them to Snarkworld, with Franklin pursuing in Friday. Jakal stole the Pack's powers, and tried to kill Snark Emperor Bhadsha, but Franklin and an escaped Kofi rescued him. Meanwhile the transferred powers proved too much for Jakal, and they reverted back, but not to the original owners. Alex gained the energy powers as Destroyer; Julie, the mass powers, becoming Molecula; Katie, the flight, to become Starstreak, while Jack became Counterweight with the gravity powers. Jakal, his brain failing, allowed the dying Bhadsha's mind to be transferred into his healthy body. Power Pack returned to Earth to be reunited with their worried parents, who learned of their unusual friends, but not their powers, at this juncture.
Soon after this, Power Pack fought Sabretooth during the Marauders massacre of the Morlocks and helped X-Factor rescue Leech and Caliban. They met the Avengers and Fantastic Four, and Mr. and Mrs. Power befriended Franklin's superpowered parents. Over the next few weeks Power Pack fought the drug dealing gang Trash and their employer, the Garbage Man, adventured with Madcap, stopped Master Mold from killing Franklin, and fought alongside X-Factor against the Horsemen of Apocalypse, preventing his ship from crashing into the Statue of Liberty. They saved the young mutant Rebecca Littlehale from her out-of-control teleportation powers, but later she was kidnapped by the Bogeyman, who tried to sell her and Starstreak to the demon N'Astirh. Though he was stopped by Power Pack and the New Mutants, he soon returned, transformed by N'Astirh into a demon, and attacked the Power family during Inferno, when demons invaded New York. To save their parents, the children were forced to reveal their powers; Margaret and James seemed unable to cope with the revelation, so the New Mutant Mirage convinced them the superpowered children were illusions she had generated to fool the Bogeyman.
In the following months the Pack met Dakota North and the Punisher, and Katie fell into an extra-dimensional pocket of her costume, ending up in Elsewhere, the realm from which the costumes were cleaned and transported. Then they visited the artificial Kymellian homeworld, where they met Force 4, Kymellian heroes, and learned that Kofi's father Yrik had brainwashed their parents to ensure the children's abilities could remain secret; it was this conditioning that had caused the adverse reactions when the powers were revealed. Angered, Power Pack and Kofi ran away, just before Maraud attacked Kymellia. Meanwhile, Power Pack encountered Numinus, cosmic embodiment of the wonders of the universe, and learned she intended them to save the Kymellians from stagnation and extinction. Returning to Kymellia, they ran into Maraud and were forced to transfer their powers to her, but when she broke her promise not to attack Kymellia again, they wrested them back.
Julie regained the flight powers, as Lightspeed; while Jack, Alex and Katie took the Destroyer, Mass Master, and Counterweight powers and names, respectively. They defeated Maraud, and the Kymellians moved from their artificial world to a verdant new planet, rejecting excessive technology. The Kymellian Technocrat, unhappy with this, kidnapped the Power adults and replaced them with artificial duplicates at an unspecified point soon after, planning to extract the matter/anti-matter process from James Power's mind. He hoped to use this to destroy the new homeworld and force his race back to an artificial one. Alex began to suspect the switch so he was also replaced. Back on Earth Power Pack fought Typhoid Mary and prevented Mysterio from frightening everyone out of their apartment building.
"Alex" began to lose his hair, his form reverting to its true appearance. Power Pack battled the son of the Star-Stalker alongside Galactus' herald Nova (Frankie Raye), an Elan child, and a fireproof tramp called Raymond. Seeing the battle on TV, "Margaret Power" had a breakdown, while "James" finally learned his children's secret. Soon after, "Alex" transformed physically into a Kymellian. Mr. Fantastic tried to return him to normal, but an attack by the Red Ghost and his Super Apes interrupted the attempt. With "Margaret" catatonic and "Alex" stuck in his alien form, the Power family traveled the world looking for a cure, meeting Excalibur in Britain and the "Monster from the Lost Lagoon" family in the Caribbean. Unable to find help on Earth, they flew to Kymellia, where Power Pack learned of the substitutions, and defeated both the Technocrat and Maraud. They switched powers around again, finally ending up with each having their original powers, and the reunited Power family returned to Earth.
Alex later stole his siblings' powers and joined the New Warriors, calling himself Powerpax and later Powerhouse; he also let his new team use Friday. Both acts angered his siblings, and when a fight with the Dire Wraith Volx destroyed the Smartship's body, Alex quit the Warriors and returned the powers to their original owners. Sometime later the Power family moved to Bainbridge Island, near Seattle, and Alex and Julie renamed themselves Zero-G and Starstreak. On Snarkworld Jakal's mind took over the Emperor's body, and he sent troops to kill them. Allied with Kofi and Sobak, a Snark, they visited Snarkworld, picking up a new body for Friday en route, and defeated Jakal again. Recently, Julie has left home and moved to Hollywood, hoping to start an acting career; there she encountered the Runaways while working with a support group for former teenage super heroes.