This quiet billionaire owns an estimated 15 percent stake in the closely held Koch Industries, the second-largest private company in America. But perhaps more notably, the septuagenarian is the only one on this year’s Forbes 400 List who can call herself Anna Nicole Smith’s former daughter-in-law. Her late husband, E. Pierce Marshall, also valued his privacy, but the couple found themselves under the klieg lights during the protracted legal battle that broke out between Pierce, his brother, and the famous Texas Playmate over the estate of multimillionaire J. Howard Marshall II, who died in 1995. This feud has spawned endless tabloid coverage and two Supreme Court cases; in the second case, Chief Justice John Roberts compared the whole imbroglio to Charles Dickens’s Bleak House. While E. Pierce Marshall died of an undisclosed infection in 2006, some of this legal wrangling continues, including a fight with the Internal Revenue Service over millions in back taxes the agency believes it is owed.