THE most vivid characters in Alan Moore's graphic novels are antiheroes of ambiguous morality and identity: costumed avengers like Rorschach, the disturbed street vigilante of "Watchmen," or the crusader known only by the letter V, who commits catastrophic acts of terrorism in the dystopian tale "V for Vendetta."With inventions like these, and a body of writing that spans nearly three decades, Mr. Moore, a 52-year-old native of Northampton, England, distinguished himself as a darkly philosophical voice in the medium of comic books — a rare talent whose work can sell solely on the strength of his name. But if Mr....