*Sonia the Hedgehog is a character that appears in the Sonic Underground television series. She is an anthropomorphic hedgehog, the middle triplet sister of Sonic and Manic the Hedgehog, and the only daughter of Queen Aleena. She is also a member of the Sonic Underground and one of the current leaders of the Freedom Fighters along with Sonic and Manic.

Sonia is an anthropomorphic hedgehog with a slim, curvy figure, bright fuchsia fur, pink hair in a style of straight spikes and full fringes, peach skin, and black eyes like her siblings.

For attire, Sonia wears a dark red, sleeveless top, a dark purple miniskirt, and a gold belt that forms a pointed shape at the front and bottom with a round, blue gem in the center of the belt. Unlike most Sonic characters who wear white cartoon-style gloves, Sonia wears long, purple ones that go halfway past her elbows. Sonia also wears red pants under her skirt with dark purple spots on the knees and a thin, purple stripe on each of her thighs, a pair of dark purple boots with red toes, and her royal medallion around her neck. In Flying Fortress, when visiting a beach, Sonia wears green sunglasses and a blue bikini with yellow stripes. In The Big Melt, she goes to the beach again and instead wears a yellow, midriff-baring t-shirt with a white stripe across the chest and a yellow bikini bottom. Sonia also has two known winter outfits, identical in appearance but with differing colors.

As Sonia was raised with luxury and wealth, she was originally quite high-maintenance, spoiled and snotty. She hates getting dirty and constantly worries about the condition of her hair and clothes. Although she appears to be selfish, she is generally good-natured and helps those that; are in need. Sonia is known to occasionally talk like a valley girl. Sonia always addresses her mother as simply "Mother" due to being raised in a polite society.

Despite all this, Sonia has been shown to like performing daring acts, such as walking on a high brick wall. She is also very athletic, and appears to be good at gymnastics. Sonia is very self-sufficient and does not hesitate in taking on any threat or challenge that she may encounter, often coming out on top. She likes to think things through and on many occasions, has helped her brothers out of their own troubles (although she sometimes thinks of them as nothing more than pains). Sonia hates messy things like dirt and mud.*