Some TMNT stuff was always meant for grownups.
HistorySavanti Romero was the former apprentice of the time lord, Lord Simultaneous, and husband of Savanti Juliet, he was once charged with the duties of maintaining the flow of time. Too ambitious and arrogant, in his thirst for power he wanted to be the ruler of all time. He once tried to turn the tables on his master by "editing out" Simultaneous out from history. His plan was discovered, and for his actions he was sentenced to death by the Council of the 79th Level, a sentence which was commuted to a lifetime banishment to 1406 A.D, where Romero, however, learned the art of black magic. As an added punishment, Lord Simultaneous changed his form into that of a demonic-like being (Transdimensional TMNT).
One day the Turtles and their new acquaintance Renet were displaced accidentally in the year 1406, right in front of Romero's castle, where they located the camp of Cerebus, who planned to besiege the castle to obtain some scrolls, which Romero had stolen. There Romero met the Turtles, Cerebus, and Renet, as he attempted to attain the Sceptre of the Sands of Time that had enabled the group to travel to that era. Romero managed to grab the Time Scepter, as the Turtles and Renet had to contend with Cerebus' help in attacking the castle. The force however, was no match for Romero's magic. He nearly succeeded, but before it came to the worst, Lord Simultaneous appeared. Romero attacked Lord Simultaneous, who took the Time Scepter once again and banished Savanti, he handed the scrolls to Cerebus, sent the Turtles back to their time again, and sent Renet to his huge library to wipe dust. Romero himself was exiled even further into the past as punishment to the Cretaceous period. (TMNT Vol. 1, #8).
In the Cretaceous, however, Romero was not idle. Savanti used his sorcery to send a magical message to the Turtles in the present, challenging them to another fight. Worrying that Savanti would corrupt the timestream, the Turtles and Renet used the Sceptre to transport to prehistoric times, where they fought Savanti again. There he kidnapped Renet and stole Time Scepter to take his ultimate revenge on the Turtles : Using the scepter as an amplifier and Renet as a victim Romero, he would use accumulated cosmic energy to have all volcanoes in the Pacific Ring of Fire erupt at the same time to allow the migration of the Earth around the sun to delay - only for a while though, but with the consequence that the meteorite, which brought about the extinction of the dinosaurs would miss, in this case the Earth would fail and thus the evolution of humans and the emergence of the Turtles from the beginning should be prevented. The Turtles managed to foil the plan; by turning Savanti’s own magic against,he fell both charred and frozen into a nearby lake. After retrieving the Sceptre, the Turtles returned to their own time (Tales of the TMNT #7). His wife, Savanti Juliet, later tried to take vengeance on them for losing her husband, but was killed by Renet.
Romero, however, had managed to survive. The Turtles were forced to confront Savanti Romero a third time when Gosei Hattori, a samurai-descendant and friend of theirs, came to them upon the feeling that history had changed. It would later be revealed that he had been cryogenically frozen in the lake he fell into previously, thawing and awakening millions of years later in fourteenth century Japan. As soon as he awoke, he began once again to lure the Turtles and Renet back to him. With Renet’s help, the Turtles transported to 1373 Japan and found Savanti Romero to have taken control of a faction of Japanese warriors as well as a dinosaur-like samurai called Chote. He had remained suspended in rock for thousands of years until he had broken free in Feudal Japan. While he succeeded in luring the Turtle to him, the Turtles regained the upper hand. The Turtles and Renet managed to subdue Savanti, and once again they banished him to prehistoric times (TMNT Vol. 1, #46 & 47).
Tales of TMNT Vol.2 # 71
In the alternative history story The Paradox of Chudnovsky, Renet and Savanti Romero were actually a couple, but their personal differences about the objectives of their studies under Lord Simultaneous ultimately led to their separation. Savanti was not cursed by Simultaneous, but physically corrupted by his investigation of the death-time. At the end of their struggle against Savanti, Renet's "Big Bang-yolk" - ("Big Bang Yolk") magically turned Savanti back into a baby.
Bebop & Rocksteady Destroy Everything!
Shortly after the events in the Cretaceous Period, Savanti met up with versions of Rocksteady and Bebop, who had become trapped in that time period and became his henchmen. After attacking an Utrom science outpost for their trans-dimensional technology, he was interrupted by a future version of Renet, whose time scepter he stole. However, he found himself pursued through the timestream by another team of Turtles, and landed in a different timeline from them.
He arrived in Rio de Janeiro and planned to reconnect with Bebop and Rocksteady. However, he encountered them prior to their adventures with him, and thus they did not know him. They easily beat him up and took the futuristic time scepter, setting off a complicated chain of events that would nearly destroy the multiverse. Savanti then escaped courtesy of an Utrom dimensional transporter.
Bebop & Rocksteady Hit The Road
He returned in the sequel Bebop & Rocksteady Hit The Road, having spent the last decade unsuccessfully attacking the Time Masters. As he still wished the pair to be his henchmen and help him kill Lord Discordance, he enchanted them with a time distortion that reverted them back to their human appearances, so that he could get them to work for him with the promise of turning them back to their mutant forms. They eagerly accepted his offer, but the Time Lords arrived to apprehend him, and Savanti quickly discovered how destructively incompetent the pair could be. His attempts to escape were fruitless, and he was arrested.
- Transdimensional Teenage Mutant Ninja Turtles gives his full name as Savanti Alfonso Juanito Geriero Santiago Romero. Although this is not indicated anywhere in any other official materials, many consider it canon for the Mirage continuity, if not overall.