Richard Branson, the 48-year- old chairman of the London-based Virgin Group, has parlayed a lifelong disdain for conventional business wisdom into a $3.5 billion international conglomerate and one of the world's most powerful and recognizable brands. Under the ubiquitous Virgin banner, Mr. Branson has ventured into a panoply of businesses - from condoms to wedding gowns, from airlines to financial services - and in the process has taken on entrenched giants and wrested market share from them.