Oxford Dictionary of National Biography
Preeminent British biographical source. Scholarly essays about deceased, noteworthy persons from the earliest times to the present who were born and lived in the British Isles or its territories or who visited or settled in the British Isles for significant periods. Also provides access to essays in the Dictionary of National Biography, published in the late 19th/early 20th century. When available, cross-links to the person's biography in the American National Biography.
The online version has shorter essays and is designed as a complement to the print version (both editions):
Dictionary of National Biography (multivolume) / REF DA 28 .D4
Oxford National Biography (multivolume) / REF DA 28 .O95 2004