Hex first appeared attempting to steal the Archamada Book of Spells. He wanted to combine its powers with the Charms of Bezel. Each charm has its own powers, including: levitation, fire, reincarnation, lightning, and luck, giving the owner incredible powers. However Ben transformed into XLR8 and defeated him. Hex lost the luck charm during the fight, and Ben gave it to Gwen as a souvenir for the fight. She discovered its powers and used it to become Lucky Girl. Hex escaped prison and attempted to steal the Archamada Book of Spells again, but realized he didn't have the luck charm and attacked Gwen to get it. He took the charm, but was defeated by Ben, Gwen and Max. Afterwards, Gwen decided to crush the charms.
Hex reappeared being broken out of prison by his niece, Charmcaster. He wanted to get revenge on Gwen for destroying the charms, but also wanted to find the Keystone of Bezel, which increases an individual's natural abilities ten times. It can also be used in a ritual to reforge the other charms. Gwen had found the Keystone and used its powers to become Lucky Girl again. Charmcaster was able to get the Keystone away from Gwen, then betrayed Hex when he started the ritual. She attempted to take the Charms for herself, but Gwen, Ben and Max stopped her. Ben used his Wildvine form to crush the charms, draining Hex and Charmcaster's powers, but not the Keystone, despite what the others thought.
Hex came back again, having aged into an old man. He is searching for the Fountain of Youth. He was able to find the Fountain, but a young Ben (having been turned into a toddler from exposed to the Fountain) transformed into Heatblast. With Gwen taunting the young Ben, he become so angry that when fighting with Hex, he evaporated the Fountain, overexposing Hex, sending him flying in the air. Hex was found by Charmcaster having been turned into a toddler. In the end, Hex was being taunted by Charmcaster, saying she is in charge now.
Ben 10 Alien Force
Like his niece, Charmcaster, Hex reappeared in the episode entitled, "Time Heals". The story begins with Gwen infiltrating his house to steal the Grimoire of Archamada, which he claimed from the original series. With Gwen's time spell, despite Paradox's warning, which she intended to use it to time travel to the past in order to prevent Ben and Kevin from hacking the Omnitrix, therefore cancelling Kevin's grotesque mutation. Though she succeeds, her action causes Hex to take over the world. Thanks to his magic, the Master magician knows that Gwen is responsible for the creation of this future, and tries to prevent her from turning the future back to normal (it is learned that he kept Ben in prison while Gwen of that timeline died in combat against Charmcaster). However, after a short fight against Charmcaster and a possessed Kevin, Gwen escapes and finds the prison, freeing Ben from captivity. Ben helps her get the Grimoire of Archamada back so she can gain enough time to go back in the past and prevent herself from changing the future. Ben's status (in this timeline) after the battle is unknown.