Rep. Bart Stupak (D-Mich.), co-chairman of the House Pro-Life Caucus, has toiled in relative obscurity through his nine terms. But he became a household name almost overnight earlier this month when he forced Speaker Nancy Pelosi (D-Calif.) to allow his strong anti-abortion amendment to the health care reform bill on the floor, banning anyone from using new federal subsidies to buy an insurance plan that covers abortions.

Stupak’s coup was months in the making. His amendment had failed by a single vote in the Energy and Commerce Committee, and he repeatedly warned House leaders that there would be trouble on the floor if they failed to allow his amendment.

Stupak had scores of backers within the Democratic Party, including some Members who warned they would vote against the bill unless Stupak’s amendment passed. Stupak, a former state trooper from Michigan’s Upper Peninsula, also had the crucial backing of the Catholic bishops, who made their support of the broader reform effort contingent on the abortion language.

During the final days of heated negotiations, Stupak returned from his mother-in-law’s funeral and quickly put the kibosh on mushier language restricting abortions that had been proposed by Rep. Brad Ellsworth (D-Ind.). And supporters of abortion rights who planned to jam Stupak on the House rule for the bill ended up getting jammed instead, including Pro-Choice Caucus Co-Chairwoman and Rules Chairwoman Louise Slaughter (D-N.Y.) and Rep. Rosa DeLauro (D-Conn.), whom Pelosi had tasked with resolving the issue.

Stupak has since become a lightning rod for criticism from the left, and his amendment kicked off a furious backlash from women’s groups that prompted President Barack Obama to take to the airwaves to say that the language needed more work so both sides could come to an agreement. About 40 abortion-rights supporters in the House vowed to oppose a final bill with the Stupak language. But with the votes so close in both chambers, Stupak will be negotiating from a position of strength.