Alejandro Jiménez Cruz was the second person to use the "Dr. Cerebro" ring name in professional wrestling, taking over both the name and the mask from José Mercado López, better known as Pentagón II / Pentagón Black upon his wrestling debut. The ring character was that of an "evil doctor", complete with wearing totally white ring gear and mask, where it looked like the top of the cranium had been removed to show the brain. On September 16, 1997 Dr. Cerebro teamed up other young wrestlers from International Wrestling Revolution Group (IWRG), Fantasy, Mr. Águila, Neblina and Tony Rivera to defeat the team of Toryumon trainees Judo Suwa, Lyguila, Magnum Tokyo, Shiima Nobunaga and Sumo Fuji to win the Copa Higher Power tournament. A few months later he competed in Toryumon's Young Dragon's Cup, defeating SAITO in the first round before losing to Magnum Tokyo in the semi-finals. On January 18, 1998 the team of Dr Cerebro, Hijo del Gladiador, El Felino, Mr. Niebla, Tigre Blanco, Tony Rivera and Venum Black lost that year's Copa Higher Power to the Toryumon team of Suwa, Lyguila, Tokyo, Saito, Fuji and their trainer Último Dragón. In early 1998 IWRG created the IWRG Intercontinental Welterweight Championship and held a month-long tournament to determine their inaugural champion. Dr. Cerebro defeated Oro, Jr. in the first round, Star Boy in the second round and finally defeated SHiima Nobunaga in the finals of the tournament to become the first ever champion. Over the summer of 1998 Dr. Cerebro began a storyline feud with the tecnico (wrestler who portrays the "good guy") Oro, Jr., starting out with being over the Welterweight championship but soon turned into a more personal storyline between the two. The storyline led to both masked men putting their mask on the line in a Luchas de Apuestas, or bet match. Dr. Cerebro won and forced Oro, Jr. to unmask and reveal his real name. He would later abandon the Oro, Jr. name all together and become known as Mike Segura. On December 13, 1998 Dr. Cerebro lost the Welterweight championship to Shiima Nobunaga. In early 1999 Dr. Cerebro traveled to Japan to compete in the Japanese Toryumon, teaming with Bombero Infernal for most of the matches as the two slowly developed into a regular tag team combination. Back in Mexico Dr. Cerebro competed in the 2000 Yamaha Cup, losing to Genki Horiguchi and Mike Segura in the first round of the tournament. The team of Dr. Cerebro and Bombero Infernal received a couple of opportunities to wrestle for the IWRG Intercontinental Tag Team Championship, but lost to the championship team of Fantasy and Star Boy. Following the Yahama Cup Dr. Cerebro began working mainly for IWRG and soon recaptured the Welterweight Championship, defeating Último Vampiro on June 29, 2000. He subsequently began a storyline feud against Ciclon Ramírez over the Welterweight Championship that had Bombero Infernal help his partner on more than one occasion. On June 15, 2000 the three were involved in a three-way Lucha de Apuestas match with Ramírez risking his mask while Dr. Cerebro and Bombero Infernal both risked their hair. The match ended with Ciclon Ramírez pinning Bombero Infernal, forcing him to have all his hair shaved off as a result of the loss. Ramírez followed up by winning the Welterweight Championship only two weeks later. The feud with Ciclon Ramírez soon segued into a feud between Dr. Cerebro and longtime rival Mike Segura. The storyline included Dr. Cerebro defeating both Ramírez and Segura in a match on August 13, 2000 to win the Welterweight Championship for the third time. He would later successfully defend the championship against Mike Segura. IWRG had a working relationship with Consejo Mundial de Lucha Libre (CMLL) that allowed CMLL wrestlers to work for IWRG as well, which brought El Hijo del Santo to IWRG and in direct conflict with Dr. Cerebro as the two clashed over the IWRG Welterweight Championship. The storyline between the two saw El Hijo del Santo win the mask of Dr. Cerebro as he won a Lucha de Apuesta match on December 21, 2000 forcing the Doctor to unmask and reveal his given name as per Lucha libre traditions. On January 10, 2002 Dr. Cerebro along with Paramedico and Cirujano defeated Los Megas (Mega, Super Mega and Ultra Mega) to win the Distrito Federal Trios Championship, making Dr. Cerebro a double champion in IWRG. Five months later Dr. Cerebro and Bombero Infernal won the IWRG Intercontinental Tag Team Championship when the champions Mega and Ultra Mega failed to appear, which meant that Dr. Cerebro held three different championships at one time.