Alien X

Alien X is the Omnitrix's DNA sample of a Celestialsapien from the Forge of Creation.

Appearance
Alien X is a humanoid alien whose entire body is solid black (excluding his hands, which are white). He has tiny white star-like spots all over his body, giving him the appearance of a starry sky. His eyes are green and pupiless, and his forehead bears three horns, (similar in shape to Ultimate Way Big's).

In Omniverse, Alien X is largely the same as before, but with a more "heroic" appearance. His chin is now bigger (like Diamondhead's), his body is more muscular, his horns are smaller, and the stars on his body are brighter than before.

Alien X wears the Prototype Omnitrix/Ultimatrix/Omnitrix symbol on his chest.

Backstory
Ben acknowledges Alien X as his most powerful alien, but concedes that transforming into him is not worth the cost.

Alien X has three personalities: Serena, the voice of love and compassion, Bellicus, the voice of rage and aggression and Ben, the voice of reason. All three speak in unison when Alien X speaks.

As Serena and Bellicus have been arguing for eternity and before they had no tiebreaker, getting them to focus on any present task is difficult at best, leaving Alien X's body trapped in place until an agreement is made.

However in Omniverse, Ben uses Alien X successfully to create a near exact copy of the universe when it gets destroyed by the Anihilaarg.

Powers and Abilities
Alien X is omnipotent, being able to warp reality, time, and space with ease. Even his mere thoughts can become real - theoretically, he can wield any and all powers in the universe if he wishes.

Alien X can create time waves to reverse events, as seen in X = Ben + 2.

Alien X can create an entire universe at will, as seen in So Long, And Thanks For All The Smoothies. He is also supremely durable - possibly being completely immortal - as he was completely unharmed when the Anihilaarg destroyed the universe around him.

As shown in Universe Vs. Tennyson, Alien X can self-duplicate and create galaxies to suck in other beings. He is also capable of high speed travel, superhuman strength, and the ability to grow to a gigantic size. He appears to be skilled at hand-to-hand combat.

Weaknesses
In order for Alien X to perform any action, including simple movement and transforming back, at least two of his personalities must agree to do so. This has proven to be a major weakness, as Serena and Bellicus weren't interested in dealing with present affairs and wanted to finish past ones that weren't possible to deal with without Ben.

In Ben 10,000 Returns, the said weakness was referenced by Professor Paradox, where he revealed that there is an alternate timeline where Albedo transformed into Negative Alien X and was stuck motionless for nearly a year.

However, it's revealed in Weapon XI: Part 1 that Ben has control over him after Universe Vs. Tennyson.

Alien X is vulnerable to having his powers absorbed, as Ben and Azmuth have implied that Darkstar and Osmosians can absorb his omnipotent powers.

In addition, other Celestialsapiens can harm Alien X, as shown in Universe Vs. Tennyson.

Alien Force

 * Alien X first appears in X = Ben + 2,
 * Alien X stops a flood caused by a broken dam. After much fruitless argument, Ben convinces Serena and Bellicus to transform him into another alien (mostly by insulting them).
 * Ben swears that he won't use Alien X again, as it is not worth the price.

Ultimate Alien

 * Alien X returned to Ultimate Alien in The Forge of Creation.
 * Ben half heartedly turned into Alien X in hopes of locating the Forge of Creation before Ultimate Aggregor could obtain the universe's greatest power. After transforming, Bellicus and Serena start debating about other things as usual. Suddenly Paradox appears, telling Ben that he would not be able to convince Bellicus and Serena to help him out today. Also, Paradox puts himself in danger by going into the presence of Bellicus and Serena who almost voted to destroy him, and changes Ben back into his human form before they could come to a vote.
 * In this episode, it was revealed that Ben had modified the Ultimatrix to lock the Alien X transformation, both to prevent him from accidentally morphing into the Celestialsapien in a battle and as a safety measure in case someone like Albedo stole the Ultimatrix. The only way to access Alien X was to use a pair of keys in Gwen and Kevin's possession.
 * In Ben 10,000 Returns,
 * Alien X was mentioned by Paradox, where in an alternate timeline, Albedo turned into Alien X and was trapped motionless for nearly a year.
 * In The Ultimate Enemy: Part 2,
 * Alien X appeared in the flashback.

Omniverse

 * Alien X returns to Omniverse in So Long, And Thanks For All The Smoothies.
 * When the Anihilaarg was activated, Ben transformed into Alien X in order to stop it. While he was too late to save the Universe from being destroyed, he did manage to convince Bellicus and Serena to recreate a near identical copy of the universe.
 * In Universe Vs. Tennyson,
 * Alien X's recreation of the universe was mentioned as the reason why Ben was being put on trial. Later, Ben transformed into Alien X to defeat the Galactic Gladiator.
 * In Weapon XI: Part 1,
 * Alien X battled the Rooters and the brainwashed Plumbers' Helpers.
 * This episode shows that Ben now has complete control of Alien X and was able to control him without confronting Bellicus and Serena first.

Ben 10: Alien Force

 * X = Ben + 2 (first appearance)

Ben 10: Ultimate Alien

 * The Forge of Creation (first re-appearance)
 * The Ultimate Enemy: Part 2 (flashback, cameo)

Ben 10: Omniverse

 * So Long, And Thanks For All The Smoothies (first re-appearance)
 * Universe Vs. Tennyson
 * Weapon XI: Part 1

Video Games

 * Ben 10 Alien Force: Vilgax Attacks (alternate timeline)

Ben 10: Alien Force

 * 4" Alien X
 * Alien X (Planetary Powder)
 * Alien X (Alien Creatures set)
 * 10 cm Alien X (DNA Alien)
 * Alien X with Goop (black version; creation transporter)
 * Alien X (Defender) with Alien Bust
 * Alien X (Alien Creation Launchers)
 * Omnitrix Hero Collection with Alien X hologram
 * Alien X (Alien Rocks)
 * Alien X (Keychain)
 * Alien X (Deluxe)

Ben 10: Ultimate Alien

 * Alien Creation Alien X and Ben
 * Alien X Defender and Vulkanus (DVD and 4 inch action figures)
 * Classic Wildmutt, Nanomech, Spidermonkey Defender and Alien X (Combo pack)

Ben 10 Alien Force: Vilgax Attacks

 * Alien X appeared in the game (only in the CGI movies/clips for Xbox 360, Wii, PS2 and PSP). He is not a playable alien, being replaced by Cannonbolt/Murk Upchuck.

Online Games

 * Ben 10 Alien Force: Alien Attack
 * FusionFall (Nano)

Etymology
His name, made up of "Alien", a reference to being an extra-terrestrial life form, and a transformation, and "X", the roman numeral for 10, and referring to his mysteriousness.

Trivia

 * Before Alien X appeared, the opening of Ben 10: Alien Force showed only a silhouette of him, after he appeared, it showed his full picture.
 * Alien X is a Nano and a former NPC in the game FusionFall.
 * In Project Exonaut, Alien X is a level 10 suit.
 * In Andreas’ Fault, a fan of Ben refers to the Alien X smoothie as a disappointment as well as saying it tastes like "filler." This is a reference to Alien X's constant standing in the series.
 * Ironically, in many promotional images of him, Alien X is posing dramatically (like in the openings to Alien Force and Ultimate Alien), while in the actual series, most of the time, he is frozen in a standing-up position.
 * In A Jolt From The Past, Rook speaks of Alien X, but believes he is just a rumor. Ben tries to convince him that Alien X is real, but Rook doesn't believe him and asks Ben to transform and show him, which Ben refused.
 * Alien X was the first alien in Alien Force to not be voiced by Dee Bradley Baker. The second was Rath, who is voiced by John DiMaggio.