Knuckles the Echidna- Is one of the main characters in the Sonic X series and is the protector of the Master Emerald. He considers Sonic to be his rival and friend.
Knuckles is around seventeen in the series and is Jake's best friend and the second in command of the team. He met Jake about four years (in Earth time) prior to the series when he saved Jake from a group of bullies and taught him how to defend himself. He later departed back to his homeworld but returned three years (in Earth time) later and met a now sixteen year old Jake and eventually he decided to stay on Earth with Jake who became not only his new friend but also his brother.
After one of their practice fights, he, Jake and Ansem were all attacked by Symbiotes and the two boys fought them off. Later the two combated them again and with help from Alice Gehabich, Ben Tennyson, Jenny Wakeman, Lilo Pelekai, Stitch, Artemis Crock, and Rattrap they were able to defeat them.
After a training session with Lea, Knuckles agreed with Ben that they didn't know for sure if they could trust him. He later trusts Lea fully after hearing the whole reason for his hatred towards Saix.
The conversation about wheter Lea can be trusted or not, Knuckles mentioned something about someone he and Jake once trusted and then were betrayed by that person.