The widespread popularity of the album eventually landed Keith at Geffen splinter DreamWorks in 1997; the label gave Dr. Octagon (retitled Dr. Octagonecologyst) its third release mid-year, adding a number of bonus cuts. In early 1999, however, Keith's alter ego Dr. Dooom unfortunately "killed off" Dr. Octagon on the opening track of First Come, First Served (released on Thornton's own Funky Ass label). Kool Keith signed to Ruffhouse/MCA for his second album under that alias, 1999's Black Elvis/Lost in Space. Records released as Kool Keith followed in 2000 (Matthew) and 2001 (Spankmaster), while the 2002 collaboration Gene appeared as KHM (Kool Keith plus H-Bomb and Marc Live). His next project was a four-rapper group named Thee Undatakerz with Keith taking on a new persona, Reverand Tom. Kool Keith Presents Thee Undatakerz hit the streets in May 2004. Keeping busy, Keith released Diesel Truckers in August of the same year with old friend/producer KutMasta Kurt.
As if 2004 weren't filled with enough Kool Keith releases, some truly oddball ones started to appear that year. The Official Space Tape borrowed from previous releases to create the ultimate Keith mixtape, the R&B-leaning Personal Album was released in a limited edition of 500 and with a high price tag, plus the Real Talk label issued Dr. Octagon, Pt. 2, an unauthorized release that had little to do with the original and was quickly pulled from the shelves by court order. The next year was much calmer with the Global Enlightenment, Pt. 1 DVD being released at the beginning of the year, followed by Lost Masters, Vol. 2 in the summer. Nogatco Rd. from 2006 introduced a new character, Mr. Nogatco (Octagon backward). The U.F.O.-obsessed album was a collaboration with producer Iz-Real. The two-CD Collabs Tape compilation and The Return of Dr. Octagon followed soon after. In early 2007 Keith was part of the reunited Ultramagnetic MC's and their new album Best Kept Secret. ~ Sean Cooper, All Music Guide