Some TMNT stuff really isn't for little kids.
In the IDW Comics Donatello, just like his brothers, is one of the reincarnated sons of Hamato Yoshi, who were murdered in medieval Japan by the Shredder. He began his new life in the present as a water turtle hatchling which was to be used as an experimental guinea pig in the laboratory of StockGen Research, Inc., Baxter Stockman's genetics laboratory for an experiment to create naturally armored super soldiers. Some ninja tried to seize the Turtles and various other research results from the laboratory, including a super solider mutagen. The intervention of his also-reborn father, now a lab rat, led to the Turtles and Splinter being wetted with a chemical cocktail that made them ultimately mutants, with more human-like bodies, cognition and speech.
In the months that followed, Donatello was extensively trained by Splinter in ninjutsu, with the bo as his personal weapon. Along with Michelangelo and Leonardo, he searched the alleys and rooftops of New York for their fourth brother, Raphael, who had been separated from them during the mutation process. Shortly after finding him, Donatello was given a purple mask as a sign of his individuality.
In the Micro-Series, Donatello made another important connection that would change his life, with scientist Harold Lillja. Though Lillja was his online nemesis, Donatello managed to convince him not to work with the morally corrupt Baxter Stockman. He later also befriended Professor Honeycutt, a Neutrino scientist whose advanced knowledge and kind spirit were of great interest to Donatello.
He suffered a terrible personal blow when he and his brothers visited a possible future in which Shredder reigned. In this possible future, Donatello was the only surviving brother, having only lived because he gave up the fight against their enemies. Donatello was contemptuous and fearful of his possible future self, later confessing that he had sometimes considered giving up just as that future self had done.
Donatello's anxiety over Krang and the Technodrome reached a fever peak in the Attack on Technodrome storyline, in which his actions diverged from his father's plans, due to Splinter's shortsighted fixation on the Shredder to the exclusion of all other threats. He contacted Shredder through the Metalhead robot, claiming to be willing to ally himself with the Foot in order to eradicate Krang and the Technodrome. Unbeknownst to Shredder, Donatello was actually enacting a plan he had concocted with Leonardo, with the goal of getting Krang and Shredder to kill one another.
However, the plan backfired, with both parties discovering they had been tricked. Donatello was savagely beaten and his shell was broken by the mutants Bebop and Rocksteady, who left him for dead. While his family grieved for him, Honeycutt discovered a faint pulse and managed to stabilize Donatello's badly broken body, even as he transferred the Turtle's soul into the Metalhead robot. Donatello struggled to get used to his strange new existence, even as Honeycutt and Lillja worked to heal his body and reunite body and soul.
Donatello joined his family in escaping the flyborgs and M.O.U.S.E.R. robots, transforming into a boat to carry his father away. He also participated in the Gauntlet ritual that pitted him against the mutant shark Bludgeon, whom he succeeded in permanently blinding. However, he received a transmission during the battle and initiated the robot's self-destruct, only to reappear in the arena as a newly-healed, flesh-and-blood Donatello. He then participated in the fight against Shredder, and witnessed his father's acceptance of the Foot Clan leadership.
Donatello then traveled to Burnow Island to assist Honeycutt in bringing the surviving Utroms out of stasis. He was horrified when the robot scientist was smashed, and desperately tried to save him.
Initially Donatello was supportive of his father's new role, but became increasingly uneasy during the Foot's war against the Street Phantoms. This came to a head when Splinter ordered the execution of Darius Dun, which horrified Donatello and his brothers, and led to them leaving the Foot and reuniting with Michelangelo in their old lair. Around the same time, Harold Lillja brutally cut off his friendship with Donatello, blaming him for the chaos that had entered his life.
His attempts to repair Metalhead also led to disaster, as Donatello discovered that a copy of his personality - dubbed Metal-Don by Michelangelo - had been left in the Metalhead chassis. Though Donatello was supportive of his robotic "twin," Metal-Don became increasingly unstable and viewed himself as a monster, eventually purging himself of all the emotions that made Donatello more than a calculating mind. Donatello became very depressed after this event.
Donatello was reunited with the Fugitoid in The Trial of Krang, when the Turtles agreed to find and return with key witnesses. He became a key factor in the prosecution of Krang, as well as masterminding the repulsion of the Malignoid swarm.
As the technician and amateur scientist among the Turtles, Donatello is also the one who sees the world the most pragmatically. He looks at the world according to numbers and tangible facts, and often discounts things that do not fit into the scientifically proven. His skepticism initially causes him to doubt that he, his brothers and their father Splinter have had a past life together, or that any kind of grand destiny is responsible for their lives.
It also causes some clashes with Leonardo, whose experiences and faith in Splinter lead him to believe in the supernatural. However, personal experiences, such as his encounter with his long-dead mother Tang Shen, lead Donatello to gradually become more open-minded. This coincides with an improvement in his relationship with his brother, whom he comforted after Leonardo was freed of his brainwashing.
His skepticism also leads to doubts in other areas of life, such as questioning whether their family has a chance of actually thwarting the various threats against them. In the Turtles in Time issue, he once confessed to having sometimes considered giving up the fight altogether.
Otherwise, Donatello as in the rest of the franchise is the usual science and technology fanatic who does not want to miss any opportunity to be able to take a closer look at his latest achievements.