"It's got to have been an influence on almost every comedy writer I know," said Steve O'Donnell, the head writer for "Late Night With David Letterman." "It's rare that you would meet a comedy writer who doesn't know who Arthur the Potted Plant is, or the kinds of esoterica in the margins that we ardently absorbed because we were scanning every page for most of our childhoods." Presiding over those margins was a 240-pound publisher who filled the office water cooler with wine and celebrated hitting the million mark in circulation by packing his staff off to Haiti, where Mad had exactly one subscriber. Few readers ever receive the kind of personal attention that Mr. Gaines lavished on him: Mr. Gaines drove to his house and handed him a subscription-renewal card. At Mad's office (on MADison Avenue, it says beneath the table of contents) Mr. Gaines was a sounding board for jokes, but left the writing and drawing to others. "My staff and contributors create the magazine," he said. "What I create is the atmosphere."