Former U.S. senator Charles H. Percy of Illinois, a dashing corporate executive whose meteoric political rise as a liberal Republican was later eclipsed by the sense that his potential went unfulfilled, died Sept. 17 at the Washington Home and Community Hospice in the District. He was 91.

He had Alzheimer’s disease, said Kate Kelly, the director of national publicity at the public broadcasting outlet WETA, whose president and chief executive is Sen. Percy’s daughter Sharon Percy Rockefeller.

For a time, not even the White House seemed beyond Sen. Percy’s reach. But his ambitions were foreclosed when he was narrowly defeated for reelection to the Senate in 1984, generally a landslide year for Republicans. His loss, after three terms, was a striking finish to the political career of a man once viewed as the heir apparent to the liberal Nelson Rockefeller wing of the GOP.

In today’s polarized political climate, Sen. Percy would be described as a rare breed — an unabashed liberal and skeptic about military spending and war.

After an arduous Depression-era upbringing, he advanced quickly as a young man through the ranks of Bell & Howell, a Chicago-based manufacturer of home-movie and other motion-picture equipment. At 29, he was the youngest chief executive of a major American corporation.

His rags-to-riches backstory, telegenic looks, resonant voice and prodigious Republican fundraising led many admirers, including Dwight D. Eisenhower, to conclude that he was of presidential timber.

He landed on the cover of Time magazine in 1964 — two years before he launched a successful Senate bid. Three years later, New York Times political columnist James Reston called Sen. Percy “the hottest political article in the Republican Party,” citing his industriousness on progressive causes such as housing for the poor.

From the moment he arrived in Washington in 1967, he staked out dovish positions on the Vietnam War and defense spending in general. He urged colleagues to think about the “diplomatic, psychological and economic” effect of their votes on military expenditures. Meanwhile, he called attention to substandard medical care and legal services for the nation’s elderly, an effort that culminated in his 1974 book “Growing Old in the Country of the Young.”

He repeatedly clashed with President Richard M. Nixon on foreign and domestic issues, including funding of an antiballistic-missile system and Nixon’s nomination of conservative judges to the U.S. Supreme Court. Sen. Percy also spoke out aggressively on the Watergate affair.

To no one’s surprise, he landed on the president’s “enemies list,” and some Republicans even urged him to switch parties. He said he was comfortable as a loner in the otherwise clubby Senate.

“I am not the cracker-barrel type,” he told the Miami Herald in 1974. “It doesn’t come naturally for me to sit around a potbellied stove in a general store.”

If there was a moment when Sen. Percy might have realized his White House ambitions, it probably came in 1976, two years after the Watergate scandal drove Nixon from office. But he took himself out of the running when President Gerald R. Ford, who had succeeded Nixon, chose to seek a full term.

The watershed 1980 elections put Ronald Reagan in the White House and Republicans in charge of the Senate. Sen. Percy became chairman of the Foreign Relations Committee.

Sen. Percy was widely viewed as a conscientious but less-than-commanding committee chairman, and though he took a keen interest in the Middle East, he was not always careful about how his statements might play to powerful constituencies, especially supporters of Israel.

In 1975, five years before he became committee chairman, Sen. Percy dismayed members of the Jewish community after he described Palestine Liberation Organization leader Yasser Arafat as a “moderate.” Sen. Percy explained that he used the term “relative moderate” and only in contrast with George Habash, whose radical PLO faction was notorious for terrorist attacks.

Sen. Percy’s insistence on his “devotion to Israel” did little to quell anger among voters upset by his criticism of the invasion of Lebanon in 1982 and of settlement building in the occupied territories — actions he saw as contrary to U.S. interests and disruptive of efforts to maintain peace between Israel and its Arab neighbors.

He made himself increasingly appetizing to challengers, and, in 1984, he lost the Senate election to Rep. Paul Simon (D-Ill.), whose campaign was spearheaded by two aggressive political consultants, David Wilhelm and David Axelrod. Axelrod later was a top adviser to Illinois Democrat Barack Obama’s successful campaigns for Senate and president.

Coincidentally, 1984 was also the year that a Percy son-in-law, Democrat John D. “Jay” Rockefeller IV, Sharon Rockefeller’s husband and then governor of West Virginia, was first elected to the Senate.

Paul Green, a political scientist at Roosevelt University in Chicago, said Sen. Percy was a “gentle soul” who “peaked early.” Green said the senator seldom positioned himself as a leader on domestic or foreign policy. “He was always Robin, never Batman,” Green said. “He was always the support player.”

After leaving office, Sen. Percy became an international-relations and trade consultant and board chairman of the Institute of International Education, an organization that administers education and cultural-exchange programs.

Charles Harting Percy was born Sept. 27, 1919, in Pensacola, Fla., and he grew up in Chicago. His father was a bank cashier, and his mother was a concert violinist. After the stock market crash of 1929, the senior Percy lost his job and life savings. Young Chuck Percy took a series of odd jobs to help support his family.

A seminal figure in his early life was Joseph McNabb, the president of Bell & Howell and a Sunday school teacher at the Percy family’s Christian Science church.

One day, Chuck Percy asked McNabb whether there might be a position at the company for his father. There was — plus a summer job for the boy. McNabb acquired a protege and the company’s future chief executive.

The future senator developed an early flair for salesmanship. He entered the University of Chicago in the late 1930s on a half-tuition scholarship. In addition to serving as captain of the water polo team and president of his fraternity, he transformed a student-run co-op into a $150,000-a-year-operation, taking home a five-figure cut of the profits.

After receiving an economics degree in 1941, Sen. Percy served in the Navy during World War II and then began working his way through the ranks of Bell & Howell.

He made an initial bid for public office in 1964, when he ran for Illinois governor and lost to incumbent Otto G. Kerner, a Democrat.

In 1966, Mr. Percy dislodged the much-older Sen. Paul Douglas (D) from his U.S. Senate seat as the nation reeled from the escalating Vietnam War and related civil disorder. Describing himself as a forward-thinking liberal, Mr. Percy ran a vigorous campaign against Douglas, who had once been his college economics professor.

Mr. Percy’s moment of political triumph was accompanied by tragedy. Two months before the election, an intruder broke into the family’s Lake Michigan estate and killed one of his 21-year-old twin daughters, Valerie, in her bedroom.

The case was never solved, and Sen. Percy alluded to the killing publicly only in the rarest of circumstances.

“I can walk in the shoes that you are walking in now,” Sen. Percy, then chairman of the Foreign Relations Committee, said in 1982 to relatives of two American churchwomen slain in El Salvador. “It’s a long, tortuous, hard path.”

His first wife, Jeanne Dickerson, whom he married in 1943, died in 1947. Three years later, he married Loraine Guyer.

Besides his wife, of Washington, survivors include two children from his first marriage, Sharon Percy Rockefeller of Washington and Charleston, W.Va., and Roger Percy of Seattle; two children from his second marriage, Gail Percy of Washington and Mark Percy of Newport Coast, Calif.; nine grandchildren; and six great-grandchildren.

In the midst of his unsuccessful candidacy for Illinois governor, Mr. Percy found himself on the cover of Time. He cut such an alluring political profile — a boyishly handsome, energetic CEO who rose to riches by dint of effort and ambition — that Time presented him as a potential presidential contender.

According to that profile, a political adviser once told the future senator that “it was to his disadvantage to be considered ‘too good to be true.’ ”

“Well,” Chuck Percy said, “that’s my imperfection.”