RUF is a German tuner that specializes in Porsche vehicles. They are notable for tuning and creating cars like the CTR, RCT and CTR2.
The character Blackbird (Tatsuya Shima) drives a 1987 RUF CTR Yellowbird, painted black (hence Blackbird). This is debatable as his car is either a Porsche 911 or an RUF CTR. In 5DX until the next game, he drives a black RUF RCT.
The brand first appears in Wangan Midnight (PS2 game) and later Wangan Midnight Maximum Tune 4 until 5DX+, replacing another Porsche based car Gemballa. Like other racing, RUF as a substitute for the Porsche models they are based on due to Porsche's exclusive to EA at the time. Beginning in Wangan Midnight Maximum Tune 6, RUF is replaced by Porsche as a result of Electronic Arts' expiration of Porsche's exclusivity deal.