Background: Rickey Nelson Henley Henderson (born December 25, 1958) is an American retired professional baseball left fielder who played in Major League Baseball (MLB) for nine teams from 1979 to 2003, including four stints with his original team, the Oakland Athletics. Nicknamed "The Man of Steal", he is widely regarded as baseball's greatest leadoff hitter and baserunner. He holds the major league records for career stolen bases, runs, unintentional walks and leadoff home runs. At the time of his last major league game in 2003, the ten-time American League (AL)
Context: In December 1984, Henderson was traded to the New York Yankees along with Bert Bradley for five players: Tim Birtsas, Jay Howell, Stan Javier, Eric Plunk, and Jose Rijo. In his first season with the Yankees he led the league in runs scored (146) and stolen bases (80), was fourth in batting average (.314), walks (99) and on-base percentage (.419), 7th in slugging (.516), 3rd in OPS (.934) and hit 24 home runs. He also won the Silver Slugger Award, and was third in the voting for the MVP award. His 146 runs scored were the most since Ted Williams had 150 in 1950, and he became the first player since Jimmie Foxx in 1939 to amass more runs scored than games played. Henderson became the first player in major league history to reach 80 stolen bases and 20 home runs in the 1985 season. He matched the feat in 1986, as did the Reds' Eric Davis; they remain the only players in major league history who are in the "20/80 club". In 1986, he led the AL in runs scored (130) and stolen bases (87) for the second year in a row, and was seventh in walks (89) and extra base hits (64) while hitting 28 home runs (9 of which led off games) and had 74 RBIs. In 1987 he had a below-average season by his standards, fueling criticism from the New York media, which had never covered Henderson or his eccentricities kindly. Yankees owner George Steinbrenner issued a press release claiming that manager Lou Piniella wanted to trade Henderson for "jaking it" (playing lackadaisically). Still, Henderson had his best on-base percentage to that point in his career (.423), with a .291 batting avg., was fifth in the AL in stolen bases (41) and hit 17 home runs despite playing only 95 games. It was the only season from 1980 to 1991 in which Henderson did not lead the AL in steals. Seattle's Harold Reynolds led the league with 60 steals; Reynolds tells the story of getting an impish phone call from Henderson after the season: "The phone rings. 'Henderson here.' I say, 'Hey, what's going on, Rickey?' I think he's calling to congratulate me, but he goes, 'Sixty stolen bases? You ought to be ashamed. Rickey would have 60 at the break.' And then click, he hung up." In 1988, Henderson led the AL in steals (93), was third in runs scored (118), fifth in OBP (.394) and seventh in walks (82), while hitting .305. Though only in New York for four and a half seasons, Henderson set the Yankees' franchise record with 326 stolen bases; the previous high (248) had been held by Hal Chase. On May 28, 2011, Henderson's total was surpassed by Derek Jeter, who'd played 1,700 more games as a Yankee than Henderson.
Question: Who signed him to the yankees?

Answer:
In December 1984, Henderson was traded to the New York Yankees along with Bert Bradley for five players: Tim Birtsas, Jay Howell, Stan Javier, Eric Plunk, and Jose Rijo.