who all are the main characters in it?
Grey, Yang, Stevens, Karev, and O'Malley.
Grey's Anatomy
Grey, Yang, Stevens, Karev, and O'Malley. 
when does lexie come in grey's anatomy The character is introduced in season three what features does this character have? Her character has been called "reliable, trustworthy, timid, and apprehensive" .The character has also been described as an "innocent young intern" she knows how to make good relationships was it a series where she appeared? Yes, a  television series "Grey's Anatomy". who directed it? Directors vary by episode, with Rob Corn directing most frequently, followed by Tom Verica. Horton, Edward Ornelas, and Jessica Yu have also directed a substantial number of episodes
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Grey's Anatomy [SEP] Main cast
The 5 characters who are first introduced in the series premiere, as surgical interns, are Grey, Yang, Stevens, Karev, and O'Malley. They are initially mentored by Bailey, a senior resident who becomes the hospital's Chief Resident, and later an attending general surgeon, in season 6. The surgical program is initially headed by Richard Webber, the Chief of Surgery, who has a pre-existing personal relationship with Meredith, having had an affair with her mother when Meredith was a child. In Webber's employ are attending neurosurgeon Derek Shepherd, dubbed 'McDreamy' by the residents, and attending cardiothoracic surgeon Preston Burke. Shepherd is introduced as Meredith's love-interest, while Burke begins a relationship with Yang.