Flair signed with the World Wrestling Federation (WWF) in September 1991 and began appearing on television with the Big Gold Belt, calling himself "The Real World Champion". Led by his "financial adviser" Bobby Heenan and his "executive consultant" Mr. Perfect, Flair repeatedly issued challenges to WWF wrestlers like "Rowdy" Roddy Piper and Hulk Hogan, wrestling a team led by Piper at Survivor Series in November 1991 and helping The Undertaker defeat Hogan for the WWF Championship that same night. WCW sued Flair in an attempt to reclaim the championship belt, but Flair claimed that he owned the title belt in lieu of the US$25,000 deposit paid by NWA champions upon winning the title, which had not been returned to him when he was fired from WCW.  At the 1992 Royal Rumble, Flair won the Rumble match to claim the vacant WWF Championship. Flair entered as number three in the Rumble match and lasted 60 minutes, last eliminating Sid Justice with help from Hulk Hogan, who had been eliminated by Justice seconds earlier. Randy Savage then challenged Flair for the WWF Championship as part of the double main event at WrestleMania VIII. In the storyline, Flair taunted Savage by claiming that he had a prior relationship with Savage's wife, Miss Elizabeth. Savage defeated Flair for the title at WrestleMania. In July 1992, as Savage prepared to defend the title against The Ultimate Warrior at SummerSlam, Flair and Mr. Perfect sowed distrust between the two by suggesting that they would back one or the other during their match. They actually attacked both Savage and Warrior and injured Savage's knee, an injury that Flair exploited to regain the title in a match with Savage on September 1. His second reign was short-lived, however, as he lost the title to Bret Hart on October 12, 1992.  Flair teamed with Razor Ramon to take on Savage and Perfect at the Survivor Series in November 1992. Flair appeared in the Royal Rumble in January 1993, then lost a Loser Leaves the WWF match to Mr. Perfect on the next night's (January 25) Monday Night Raw in a match taped six days earlier. Flair then fulfilled his remaining house show commitments, making his last appearance on February 10, 1993, before returning to WCW.

Answer this question "who were some of his matches against?" by extracting the answer from the text above.
repeatedly issued challenges to WWF wrestlers like "Rowdy" Roddy Piper and Hulk Hogan,