When renowned cellist Mstislav Rostropovich died less than a year ago at the age of eighty, the world lost not only an extraordinary musician but an accomplished conductor, an outsize personality, and a courageous human being. "It is not an exaggeration to say that the history of the cello in the twentieth century would be unthinkable without the name of Mstislav Rostropovich," writes Elizabeth Wilson. "He has seemed to me like a personification of the cello itself." Ms. Wilson, a former student...