When artist Ralph Steadman does an impression of his late gonzo co-conspirator Hunter S. Thompson—as he often does—the sound he makes is more canine than human.  “Ralph! Ralph!” he barks in an irritated monotone, affectionately mimicking the author’s voice. “Why don’t you give up writing and stick to your scribbling!” Steadman, who turns 90 on May 15, has now outlived Thompson by 21 years, but their friendship and many collaborations represent some of the central events of his life. Together, combining Steadman’s drawings with Thompson’s words, they made some alarming literary history, delivering savage humor with a harsh, critical look at contemporary society, politics, sports, war, and peace. Their books included Fear and Loathing in Las Ve gas, Fear and Loathing on the Campaign Trail ’ 72 , and The Curse of Lono , plus many articles for Rolling Stone and various other publications.…