The Birth of Gio: The Fifth Turtle by K. A. Korstjens

After years of perpetual and continuous failure in capturing and disposing of the Turtles, Krang approached the Shredder with a new plan. Krang proposed that they genetically engineer an equal to their four nemeses – a Genetically Engineered Opponent, or GEO for short.
Though somewhat skeptical of this plan, the Shredder reluctantly agreed to venture down this avenue as all other options had been exhausted.
Krang and the Shredder arranged a trap for the Turtles -- using the combined incompetence of Rocksteady and Bebop and the skills of the Foot -- whereby they would obtain blood samples from each of the four and use the genetic material to manufacture GEO.
The trap didn't go quite as expected, yet they managed to ascertain what they were after.
Krang immediately went to extracting the DNA from each sample and infusing the separate strands into the subject turtle, thereby allowing GEO to match each of the Turtles' abilities. Krang used the same gelatinous, hazardous material that created his foes in the beginning. The result was astounding.
GEO was unlike anything they had imagined: fast, intelligent, agile.
Krang taught GEO tactics and quick thinking while the Shredder taught him the ways of martial arts and weaponry. He trained with the Foot, but that proved to be nothing more than a warm up as he made short order of any who faced him.
After a long while, the day Krang and the Shredder had waited for had finally arrived: the day when they would let loose GEO on the Turtles. Armed with his weapons of choice, a Naginata and Hook Swords, GEO set out to find his enemies.
The first meeting of the two sides was brief and painful.
GEO managed to out-maneuver, out-think and out-perform the Turtles in nearly every way, forcing them to retreat and take the news of this new "turtle" to Master Splinter.
Splinter was just as surprised as his boys, but he quickly developed a plan to turn the tables. He told the Turtles to not harm this new brother, but instead try to convince him of the evil of his masters. The Turtles knew this would be no easy task, but they agreed to adhere to Master Splinter's request.
The next time the two parties met, Master Splinter's plan was put into action; and it was an utter failure. GEO never responded to anything the Turtles said to him, it seemed only to enrage him further.
After countless battles with GEO, it was Leonardo that finally broke through the brainwashing and convinced GEO that Krang and the Shredder were the bad guys, not them. Leonardo told GEO that they wanted him to become his brother and become a family, not bitter enemies. GEO hesitantly agreed to return to the Turtles lair to see Master Splinter.
Splinter spoke with GEO for some time and eventually convinced him to join their family.
When GEO finally agreed, Master Splinter brought out a book and handed it to GEO: The Lives of the Most Excellent Painters, Sculptors and Architects by Giorgio Vasari.
When GEO asked what the book was, Splinter told him that it was from this book that he chose the names of the Turtles – Leonardo, Donatello, Raphael and Michelangelo. Giorgio Vasari had written the tome as a collective of all the great artisans that had preceded him and just as Vasari had combined the great masters into one entity, so, too, was GEO the collective of the Turtles. It was then that Splinter told GEO that his name would longer be a mere acronym that stemmed from an evil plot, but it now would have meaning and tie him to his new brothers.
His name would become Giorgio.

This figure is just a complete repaint of the Nickelodeon Donatello. Minor modifications to the belt and strap. Original story by my personal friend K. A. Korstjens