Amy Rose is a pink, female hedgehog who has chased Sonic in love and has been trying to win his heart by any means, including impressing him by fighting robots, and jokingly threatening to keep him locked in prison. She was the first female character introduced, being introduced in 1993, into the Sonic universe and is also one of the most popular, coming in fifth place on an official popularity poll.
Like Sonic and other characters in the series, Amy is significantly shorter and lighter than humans her same age. She is 12 years old, 90 cm (2'11") tall (although sometimes it looks as if she's almost the same height as Sonic), and keeps her weight a secret.  She was described as being 8 years old in Sonic CD, but from Sonic Adventure onwards she has grown older (by 4 years). Also, with the addition of Cream the Rabbit, Amy seems to have found herself a sidekick similar to Sonic's own Tails (as implied in Sonic Battle, Sonic Heroes, Sonic Advance 3, and Shadow the Hedgehog).
Since her appeareance in Sonic Adventure, Amy became one of the main characters of the series, and has appeared in nearly every Sonic game since, as well as the TV series Sonic X.
Amy in the main series is presented as being somewhat kind and sweet. In Sonic CD, she was referred to as an "optimistic tomboy" who loves fortunes and uses tarot cards. Because of her tomboyish nature, she became a playable character as a fighter in Sonic the Fighters. However, after Sonic Adventure, Amy had grown a more girly personality, such as an interest in shopping and fashion, but that didn't remove her tomboyish nature, in the more recent games, Amy has become far more violent and aggressive, much to Sonic's dismay. She often shows her anger by pulling out her Piko Piko Hammer out of nowhere and usually threatens that she'll hit Sonic with it, which causes him to run away.
Amy seems to be a girly-girl and a tomboy, such as in Sonic Battle, her attraction towards "Boxercise" plays to both elements of her ever-changing personality; the exercise helping her lose weight to maintain her girlish figure, and the boxing to help her train when she's forced to fight. In Sonic Battle she had shown a very powerful and aggressive attitude, always willing to fight, she had been training to fight by using weights. Amy is not against fighting and can fight when she needs to.
Despite her violent tendencies, Amy has a very good heart, she never gives up, and is one of the most optimistic and cheerful characters of the series. Amy is always full of hope and is always cheering on for the good side of things. She almost never seems to find anything hopeless. In Sonic Adventure, she was determined to help the Flicky who had lost his family.
In Sonic Adventure 2, Amy felt strongly that there was a chance for the world to be saved and that people were basically good (as she told Shadow). Amy is also a rather likable person. Despite her being slightly annoying, she has rarely met anyone who she did not befriend (including Shadow and Blaze). Amy is a regular sweetheart, but with a strong sense of justice, a slightly tomboyish but more girly nature, and an over sweeping infatuation for Sonic.
Since 2010, after the release of Sonic Free Riders Amy seems to be more bossy and infatuated with Sonic than before, this is probably due to the reason that Sonic games since then were more light and humorous. Amy's personality has added more a humor factor in games like Sonic Colors, Sonic Free Riders and Sonic Generations with her obsession for Sonic, which causes her to say silly and embarrassing things that she does not find very embarrassing, however Sonic responds in an awkward, embarrassed and confused way.