Cockburn, Sir Alexander James Edmund, 1802–80, British jurist. He was called to the bar in 1829, and a volume of reports on election cases (1832) brought him into national prominence as a trial lawyer. He was made recorder for Southampton (1841) and was elected to Parliament from there (1847). He was noted particularly for his defense advocacy, one of his most famous successes being the acquittal (1843) of Daniel McNaghten, who had killed Sir Robert Peel's secretary, on grounds of insanity; the "McNaghten rules" became the basic definition of criminal responsibility in most English-speaking jurisdictions. In Parliament, Cockburn successfully defended Lord Palmerston's handling of the "Don Pacifico" dispute (1850). He served as attorney general (1851–56) and was chief justice of common pleas (1856–59) and lord chief justice (1859–80), presiding over the famous Tichborne case.