Gwendolyn Tennyson is the better half of Ben 10's team. She is the brains, and he is the brawn. As Gwen has gotten older and matured more, she has become romantically attracted to ex-con Kevin Levin whom is now her boyfriend, she is considered a extremely powerful spellcaster.
Originally just an ordinary 10-year-old girl, Gwen Tennyson is the cousin and partner of Earth's greatest hero, Ben 10. While at odds with her cousin and always trying to show him up in everything, Gwen has learned that when it is time to save the Earth, she must put her differences aside and finally come to terms that her cousin is a super hero. When she was used more for information in Ben's team, she learned magic and gained the ability to be claimed as one of the most powerful sorcerers in the world, third only two Charmcaster and Hex. Now a young adult, she has joined Ben accompanied by Kevin Levin to fight off even greater threats that seem to either destroy or conquer Earth. She is romantically attached to Kevin and has put her differences aside with Ben, as they both have agreed that their childish namecalling of one another has grown old since they are now practically adults. Gwen is now a senior member of the Plumbers as well as the guardian of Magic in the Earth realm.
Gwen Tennyson, along with the entire Ben 10 franchise was created by four men, that go by the handle "Man of Action." These four men Duncan Rouleau, Joe Casey, Joe Kelly and Steven T. Seagle consist of both writers and artist who are dedicated to delivering good action packed media to children and adults of all ages. Since the beginning series Ben 10's national success, the Men of Action have used their publicity with Ben 10 to create toys, comics and video games for Ben 10. When Ben 10's series ended in the mid 2000's, the Men of Action immediately started to write the script with 5th unofficial Man of Action member, the late Dwayne McDuffie, to create the 2nd and 3rd generation of Ben 10 series which was titled Ben 10: Alien Force and Ben 10: Ultimate Alien.
Gwendolyn Tennyson is the cousin of Ben Tennyson (also known as Ben 10), and is the Granddaughter of Maxwell Tennyson. In the Ben 10 series, Gwen's role in the show was a tracker of strange events that happened on earth, she did this via her laptop. Eventually in the series, it turns out that Gwen and Ben hate each other because they both were born on the same day. That is why she ridicules him with dimwitted comments. As the series progressed, Gwen eventually trained herself in magic when she went to a magic market. She instantly gained magical abilities which gave her the power to do naturally anything. When Gwen found out that she had to loose he "special powers", she was grieved. Missing her powers, she began to search for other magical items, Gwen eventually came across a Book that was the ultimate source for magic. She was teased by Charmcaster (Gwen's arch Enemy) who mocked her of not reading the more dangerous pages, Gwen never had the courage enough to read the dangerous sections of the book, however she made an exception for one time only so that she can defeat Charmcaster. Her adventures with Ben and Max has taken her many places with them through space and time. Learning about her future as well as Ben's. Seeing that most of the character development that the Men of Action had created for the character did not stick with the future TV show, as her and Ben's future was all in an Alternate Reality.
In a alternate future. Gwen Tennson is 30-years-old and has read the entire book of Magic, she is a 10th level Black belt, and also has the 8 magical artifacts on her arm (four on each side). The world is still being attacked by aliens, and the earth has colonized with aliens so that both can live without destruction and dismay. However, the earth isn't without it's heroes. Ben 10,000 is on the case and he is nastier than Ben from the original TV show. Ben of the Alternate future is mostly isolated from his family, however when his cousin brought back Ben and Gwen of the past he eventually changed his attitude.
Near the end of the summer adventure with the trio, Max, Ben and Gwen had to defeat their most powerful foe who has swore revenge on Ben multiple times -- Vilgax! As Vilgax had a plan to destroy Ben and the Omnitrix in one plan, it took Ben realizing that he wasn't as smart as he claimed to be and that he needed the help of his family to defeat a now super powered Vilgax. This strengthened the relationship between Ben and Gwen. As both of them had been jerks all summer long, but after the finally defeated Vilgax, they knew that their adventures together would finally stop as their were no other threats to harm Earth or their galaxy.
There were already heroes and the Plumbers were more placed throughout the galaxy making sure that no threat would ever need Ben and his team to ever come help again. With that news, the summer vacation was over Ben, Gwen, and Max decided to stop fighting monsters, aliens, and wizards. This was stated as the retirement of the three heroes, and also the end of the TV Show.
5 years after the events of saving the entire universe from Vilgax, Gwen, Ben and Max had all retired to live normal lives without the constant thought of fighting against aliens and monsters on a daily basis. With Ben having finally removed the omnitrix off of his wrist, he began to play sports and just be a regular teenager. Now, 15 Gwen began to become more athletic and joined a martial arts group to learn how to defend herself if she ever needed it. While being a woman, Gwen has a black belt in karate and is possibly the best fighter in her town of Bellwood. When Max sent a message to Ben saying that he needed help and lied that he had the Omnitrix, Ben asked Gwen for advice on what to do. Telling Ben that the right thing to do was to help Grandpa Max defeat a new threat to Earth, Ben and Gwen began their team once again. In the later events, Kevin Levin was attracted to Gwen Tennyson and wanted to join Ben's team only because he wanted to fulfill a promise to his dad as well as get closer to Gwen. Through the different events that lead up to Gwen helping Ben and Kevin defeat the DNA Aliens and their dark masters, the Hybrid, she began to find out her true origins.
From a visit from Max Tennyson's ex-wife, Verdona, Gwen and Ben's grandmother, she told Gwen that her powers all come from her being 3/4 of an Anodite -- One of the most powerful aliens in the Universe. Saying that Gwen needs to leave with her to train for 75 years learning how to manipulate the so-called "mana" of the universe, Gwen refused and Verdona was enraged. Eventually defeated by Gwen, Verdona knew that Gwen was right and needed to live with Earth people and not train to use her powers. From this revelation, Gwen was explained by Hex (Earth's greatest evil sorcerer) that her alien powers are also connected to the magic realm. Meaning that the powers that Gwen holds within her also are used by the multiple magic users in the universe, seeing that they either are part anodite or they have learned the dark arts to tap into the power that the Anodites use on their home world. Eventually, Gwen and Kevin started dating again and yet another threat came to attack Earth.
Vilgax had finally come back from taking over 10 alien worlds and was looking to settle an old score against Gwen and Ben. As he was even more powerful Gwen, Ben and Kevin found out how to defeat Vilgax with the help of Max Tennyson. From there, the world found out that aliens do exist and also of the powers that Earth's protectors (Gwen, Ben and Kevin) possess.