Roy Sievers of the Washington Senators, right, with Mickey Mantle of the New York Yankees in 1958. (AP/AP)

Roy Sievers, a powerful slugger who was the brightest star of the hapless Washington Senators in the late 1950s and one of the most feared home run hitters of his time, died April 3 at his home in Spanish Lake, Mo. He was 90.

The St. Louis Post-Dispatch first reported his death. The cause was not disclosed.

Mr. Sievers came into baseball with a splash in 1949, winning the American League’s first Rookie of the Year Award with his hometown St. Louis Browns.

After injuring his shoulder, Mr. Sievers was traded to the Senators before the 1954 season. He promptly became the most prolific power hitter in the team’s history.

Despite playing his home games in cavernous Griffith Stadium, the right-handed-hitting Mr. Sievers set a new team record for home runs in each of his first four seasons in Washington, hitting 24, 25, 29 and 42 in succession.

Roy Sievers shown in 1960, when he played for the Chicago White Sox (AP/AP)

“He was larger than life,” broadcaster and baseball historian Phil Wood said Wednesday in an interview. “When you’ve got a chronic second-division club, you’ve got to give people a reason to come to the park. Roy Sievers was the reason you went to a Senators game.”

Mr. Sievers, who was primarily a left fielder in Washington, had his finest season in 1957, when he hit for a .301 average and belted 42 homers. It marked the first time any Senator had led the American League in that category. The two players who finished behind him were Hall of Famers Ted Williams and Mickey Mantle.

Mr. Sievers also led the league in runs batted in with 114, becoming the first player for a last-place team to win baseball’s home run and RBI titles. (The Senators finished the season with a 55-99 record, 43 games behind the pennant-winning New York Yankees.)

Six of Mr. Sievers’s homers in 1957 were game-winners — now often called “walk-off” home runs. The most dramatic came on Aug. 3, when his blow against the Detroit Tigers won the game in the 17th inning.

It was the sixth consecutive game in which Mr. Sievers had homered, tying the American League record of the time. (The major league record of eight straight games with a home run was set by Dale Long of the Pittsburgh Pirates in 1956. The Yankees’ Don Mattingly tied the record in 1987.)

During Mr. Sievers’s six-game homer streak, Washington Post sports columnist Bob Addie called him “the hottest thing in town outside of a laundry with no air conditioning.”

Mr. Sievers was named to the All Star team in 1957 and finished third in the league’s Most Valuable Player voting, behind Williams and Mantle.

Roy Sievers, center, at Washington’s Griffith Stadium in 1957 with Vice President Richard M. Nixon, right, and Rep. Leslie C. Arends (R-Ill.), left. (Charles Gorry/AP)

Near the end of the season, Mr. Sievers was feted with a special evening at Griffith Stadium, complete with gifts that included a Mercury station wagon, golf clubs, a clock radio, tricycles for his children and a year’s worth of free haircuts.

The master of ceremonies was Vice President Richard M. Nixon, who often said Mr. Sievers was his favorite player. As he looked out at the crowd, the usually taciturn Mr. Sievers broke down, saying, “This is the most memorable night of my life.”

Roy Edward Sievers was born Nov. 18, 1926, in St. Louis. His father, who had a professional tryout as a pitcher, worked for an iron supply company.

Mr. Sievers grew up three blocks from Sportsman’s Park, where both the Browns and Cardinals played. He modeled his swing, often described as one of the prettiest in baseball, after that of 1930s Cardinals star Joe Medwick.

Three of Mr. Sievers’s teammates at St. Louis’s Beaumont High School also became major league players, and a member of the school’s junior varsity squad at the time was Earl Weaver, future manager of the Baltimore Orioles.

Mr. Sievers was signed to a professional contract by the Browns in 1944, then served two years in the Army before beginning his minor league career. He became the Browns’ standout hitter as a rookie in 1949, with a .306 average, 16 homers and 91 RBIs.

“He has great power, can run like a deer,” Browns manager Zack Taylor said in the florid sports language of the time, “and is one of the sweetest flyhawks in the league.”

After a serious shoulder injury in 1951, Mr. Sievers underwent what was then considered experimental surgery and was told he would never play in the outfield again. When he arrived in Washington in 1954, manager Bucky Harris showed confidence in Mr. Sievers, telling him to toss the ball sidearm until he regained his throwing strength.

After his stellar season in 1957, Mr. Sievers was rewarded with his highest salary as a player, $36,000. He had 39 home runs and 108 RBIs in 1958 before being slowed by injuries.

From 1954 through 1959, Mr. Sievers hit 180 home runs for the Senators, the most of any player before the franchise moved to Minnesota in 1961.

He had productive years with the Chicago White Sox and Philadelphia Phillies before ending his career in Washington in 1964 and 1965 with the second-generation Senators. He retired with 318 home runs and was an All Star in four seasons

After his playing career, Mr. Sievers was a coach with the Cincinnati Reds and managed in the New York Mets and Oakland A’s minor league systems. He then returned to St. Louis to work for a trucking firm.

His wife of more than 50 years, Joan D. Colburn, died in 2006. A son, David Sievers, died in 1999.

Survivors include two children; a brother; two grandchildren; and two great-grandchildren.

In the 1958 movie “Damn Yankees,” about a fan who makes a deal with the devil to help the Senators win the pennant, Mr. Sievers’s swing was shown whenever the central character, played by Tab Hunter, came up to bat.

Even though the Senators were bottom-dwellers in the American League, Mr. Sievers enjoyed his years in Washington, where he met four presidents and scores of dignitaries.

“If I could turn back the clock,” he told The Post in 1964, “I’d like to go back to my Washington days. They were the happiest days of my baseball career.”