William E. Simon, Jr. (born June 20, 1951), best known as Bill Simon, is an American businessman and politician. Simon was born in Neptune, New Jersey, the son of William E. Simon, Sr, the 63rd Secretary of the Treasury under Richard Nixon and Gerald Ford.

Simon earned a B.A from Williams College in 1973 and a J.D from Boston College in 1982. From 1986 to 1988, Simon served as Assistant United States Attorney for the Southern District of New York, working under then-U.S. Attorney Rudolph Giuliani.

In 2002, Simon campaigned unsuccessfully for Governor of California as a Republican against Democratic incumbent Gray Davis. Billed as a "conservative Republican," the virtually unknown Simon's campaign was significantly boosted by support from better-known Republican officeholders from out of state, including former New York City Mayor Rudolph Giuliani.

Simon won the Republican nomination in the primary election of March 2002, in large part because the incumbent Governor, Gray Davis, launched a preemptive campaign against Simon's major primary opponent, former Los Angeles mayor Richard Riordan, a moderate Republican, whom Davis considered a more formidable opponent. Both Riordan and Simon are Roman Catholics, with Riordan pro-choice on abortion, and Simon, a Knight of Malta, pro-life.

Davis's campaign advertisements made heavy use of scandals relating to alleged mismanagement of Simon's business and charities, though one of the major court rulings unfavorable to Simon was since overturned.

In August 2002, a California Superior Court jury found Simon's company guilty of defrauding an estranged business partner in a civil lawsuit and ordered him to pay $78 million in damages. The jury ruled that Simon's company, William E. Simon & Sons, defrauded Paul Hindelang, Jr., a convicted drug trafficker, in a deal to take over Hindelang's pay phone company, Pacific Coin. The jury found that Simon's company hid its plans to expand and take Hindelang's company public against his wishes, and that Pacific Coin collapsed under the weight of the debt that Simon's company piled on it in its attempts to expand the pay phone service. Simon, co-chair of Simon & Sons, was not named as a defendant in the case and has said that he was not involved in the daily management of the firm. The judge overturned the jury's verdict; as of August 2003, the case was still on appeal.

Simon's campaign centered largely on allegations of corruption in the incumbent's administration and Davis's handling of the 2001 energy crisis.

Despite Davis' high disapproval ratings, he managed to defeat Simon by a margin of 47.4% of the vote to Simon's 42.4%. Simon was widely viewed as running an ineffective campaign, his first run for public office.

When the 2003 California recall became a reality, Simon announced he would once again be a candidate for California Governor, but ran for only a short time after qualifying for the ballot before withdrawing from the race August 23, 2003. He said, "There are too many Republicans in this race and the people of our state simply cannot risk a continuation of the Gray Davis legacy." Simon did not endorse any candidates at the time, but several weeks later, he endorsed front-runner Arnold Schwarzenegger. Despite dropping out, his name still appeared in the ballot, and he placed 12th in a field of 135 candidates.