Julie Yamamoto is the supporting of the Ben 10 franchise. She used to be Ben's girlfriend before they broke up on good terms. She first appeared in Ben 10 Returns: Part 1 at Ben's soccer game to congratulate him on his game-winning goalie work. She later broke up with Ben some time between The Ultimate Enemy: Part 2 and Rules Of Engagement.
Julie was the girl that Ben developed an attraction on. Ben met her after one of his soccer matches. The two developed a quick interest in each other, but Ben started hesitating to make any approach, afraid she might reject him if she found out about the Omnitrix. When this eventually happened during their first date, Julie turned out to not be scared of him, and they ended up in a relationship. Though non-powered at first, Julie can rely on the support of Ship, a Galvanic Mechamorph pet she met and tamed after her first date with Ben, to assist her in fights.
- According to Dwayne McDuffie, Julie's family is from Denver.
- It was revealed in Rules of Engagement that Julie doesn't like Mr. Smoothy anymore.
- Julie owns a motorized scooter.
- Gwen considers that Julie is the "only one who has common sense among the four of [them]," as she always avoids trouble in every situation.
- Like Ben, Julie likes chili fries.
- Yamamoto in Japanese means 'one who lives in the mountains’ or ‘at the foot of the mountain’, this is one of the ten most common surnames; it is found predominantly in central and west-central Japan.
- Ben accidentally broke up with her over the phone while playing a video game of Sumo Slammers. Julie had believed that Ben's rude comments towards a game character were directed towards her instead.