Boston Legal is an American legal-comedy-drama created by David E. Kelley. The series, starring James Spader, with Candice Bergen, and William Shatner, was produced in association with 20th Century Fox Television for the ABC. Boston Legal aired from October 3, 2004, to December 8, 2008. The series is a spin-off of the Kelley series The Practice, and features Practice actors including Spader, Rhona Mitra, Lake Bell, and Shatner. It is set at the legal firm of Crane, Poole & Schmidt.

The following characters originated during the eighth season of The Practice, before appearing as part of Boston Legal's regular ensemble. Both Spader and Mitra were main Practice cast members, while Lake Bell and William Shatner recurred in the series' final episodes.

Alan Shore is a brilliant lawyer with a strong moral core who nevertheless is not above obtaining ethical outcomes through unethical means. Illicit computer hacking, blackmail, disguise and bribery are all tools he uses without hesitation. Alan is, however, unwavering in his defense of the underdog (unless he is representing the other party). He is disappointed and disillusioned with how the country has changed in recent years, and routinely confronts these issues in open court. Wherever he works, he treats his coworkers with levity and refuses to take himself too seriously. Alan suffers from night terrors, has a fear of clowns, and gave up his home, preferring instead to live in hotels. He has resigned himself to the fact that he will never be made partner at the firm due to his unpredictable behavior and lack of trustworthiness; while the managing partners of Crane, Poole & Schmidt do not fully trust Alan, they do recognize his talent as an attorney. Alan is best friends with (and later husband of) Denny Crane despite their sharp differences in political ideologies.

Tara Wilson first appeared as a paralegal at Young, Frutt & Berlutti. Fired from the firm after notifying Alan of his impending dismissal, Tara is hired to work at Crane, Poole & Schmidt, the firm representing Alan's civil case. Subsequently, she became a lawyer. Tara and Alan finally began a sexual relationship following his break-up with Sally Heep, though their relationship hit a rocky patch when he hired a group of men to attack a man he had previously fought with. When Tara reconnects with one of her ex-boyfriends, the two break up, and she promptly resigns from Crane, Poole & Schmidt. Her departure leads to Alan questioning his emotional suitability for a relationship.

Sally Heep first appeared as an associate at Crane, Poole & Schmidt. Introduced in The Practice, Sally began a relationship with Alan that crossed over into Boston Legal. However, after he used her to get information from a witness against their client so they could suppress his testimony, she broke up with him. Shortly after Shirley took over the Boston offices, she fired Sally for repeated errors in case preparation that called her competence as a lawyer into question. Sally returns in Season three as opposing counsel (“Whose God Is It Anyway?” and “The Verdict”).

A named partner of Crane, Poole & Schmidt, Dennis 'Denny' Crane is a renowned attorney of some fifty years of practice who claims he has never lost a case, and never will. He is an eccentric who considers himself a legend and loves to say his own name to "sign" his verbal utterances. In one of the final episodes of The Practice, he explained that often people don't believe they're in the room with a legend, so he says his own name to let them know it's true. Denny suffers from memory loss and confusion as part of the early stages of Alzheimer's disease, but often refers to his troubles as "mad cow disease" when his utterances are confusing to others or when he himself becomes confused. While he is still trying cases frequently as late as Season 1 of Boston Legal, by Season 2, he seems to have lost most of his talent for complex litigation, though he still shows flair in appealing to a jury in closing arguments. By Season 3 he mostly serves as a figurehead at the firm, rarely trying cases and appearing in court more often as a plaintiff and defendant due to his antics. When he does appear in court as a lawyer in later seasons, however, he still performs well.

Denny is a conservative who loves firearms and believes gun control is for "communists". He also refuses to defend anyone who is accused of extremely heinous acts; in one episode, he shoots a client because of the nature of his crime (raping and murdering a child). This is just one of several people he shoots over the course of the series, with several characters saying that Denny "shoots people". Denny enjoys an extremely close friendship with Alan Shore, is also a womanizer like Alan, and has no problem sleeping with the wives of judges and clients. Though he marries another woman in Season 2 (from whom he is quickly divorced after engaging in an act of infidelity at their wedding reception), he still pines for Shirley Schmidt. Denny and Alan marry in the series finale.

The following characters first appeared in Boston Legal, and formed part of the regular ensemble. The original cast includes Spader, Bell, Mitra, Shatner, Monica Potter, and Mark Valley. Candice Bergen joined the ensemble during season one, while René Auberjonois recurred for a short time before being promoted to series regular. Julie Bowen, Justin Mentell and Ryan Michelle Bathe joined the series in the second season, while Craig Bierko, Constance Zimmer, and Gary Anthony Williams first appeared in season three. John Larroquette, Saffron Burrows, Tara Summers, and Taraji Henson joined the series in season four, as did Christian Clemenson, who had recurred since season two.