Big Bird's appearance has changed over the years, as has his personality. He originally had very few feathers on top of his head; his body feathers were also more shaggy and unkempt, and his body was not as rounded and full as it is now. His personality was more dopey and "bird-brained" than it later became. He gradually got more feathers on top, giving his head a more rounded appearance, and developed a blaze-like crest of lighter yellow feathers above his eyes. His body got fluffier, rounder and more well groomed as well. His personality developed over time from being a dim, slow-witted character into the childlike innocence he is known for today. Although all the "Sesame Street" Muppet characters are technically ageless, Big Bird is psychologically written to represent a six-year-old.