It is a big round seal of the color grey. At the middle is the Forever Knights' infinity symbol. Dotted around it are symbols written in mystic runes.
The main purpose of the Seal was to act as the prison for the Lucubras and the Diagon that Sir George had trapped.
It first appeared in the episode The Creature from Beyond where Sir Reginald made a hole in it (believing a weapons cache was on the other side), which allowed a Lucubra to escape. At the place the Forever Knights arrived and so did Ben's Team. After a truce, Gwen and Winston, the squire of Sir Reginald, started studying the Seal and deduced it was made by ancient magic to cage something. By using her magic, Gwen is able to replicate the seal and are able to trap the Lucubra back into the seal. At the end of the episode Old George approaches the place where the seal has been damaged and is saddened.
In A Knight to Remember, Ben's team and Old George come to the place where the seal is where they find Vilgax, who has absorbed Diagon's heart and is trying to destroy the seal to garner more power. Ben as Eatle and Kevin try to battle him but they are squatted aside easily. Eventually this is revealed to be a plan of Diagon's, and Vilgax is sucked into Diagon's own dimension.
In Solitary Alignment George wields Ascalon as soon as Vilgax had been sucked into Diagon's World. He goes inside the Seal but he fails to find the Diagon. He then after briefly fighting Ben, teleports away. It is at this place where Azmuth recounts his life and tells the group about Ascalon.
In The Beginning of the End, Sir George and a group of knights arrive at the place where the Seal stands as the war against the Esoterica goes on. Vilgax manages to crack the surrounding area around the Seal leading to a passage to Diagon's world however, the Seal remains enact. Ben's team arrive to help and come at the place where the Seal stands. They find Vilgax who is now the herald of Diagon having defeated a group of knights and he gets ready to battle George.
In The Ultimate Enemy: Part 1, the battle between Ben, Gwen, Kevin, George, and the Forever Knights against the Esoterica and Vilgax goes on. The battle is carried out around the Seal. Eventually, at the end of the episode the Seal cracks and Diagon frees himself. Boasting that he is everywhere, he prepares for his final plan.
Ben 10: Ultimate Alien
- The Creature from Beyond
- A Knight to Remember
- Solitary Alignment
- The Beginning of the End
- The Ultimate Enemy: Part 1 (destroyed)