Donnie

Donatello's characterization more closely aligns with his mischievous 1990s film iteration than his soft-spoken 2003 iteration. The fact that he is only a teenager learning everything on the fly is heavily emphasized and he frequently answers questions from his brothers with sarcastic and outlandish responses before yelling that he doesn't know.

He is much more high-strung and quick to anger than any of his previous iterations. He frequently gets frustrated when he can't accomplish a task. He can be defensive and argumentative, especially when his intellect is challenged (though ironically with Fugitoid, they both get along really well). He has been known to lash out whenever someone messes with his inventions or experiments, especially Mikey, but it's often verbal rather than physical. Despite this, Donnie is overall a compassionate character and would support his family and allies anytime.

That said, he is still incredibly intelligent. He is frequently praised for having "a way with machines". He is a skilled scientist, engineer, and mathematician. He begins to devote more of his time to studying technology, biology, physics, chemistry, mathematics, metallurgy, and eventually astronomy (as of Season 4) than ninjutsu.

Although he is a skilled martial artist, he often puts more faith in his high-tech gadgets and machinery than spiritual advice and traditional ninjutsu methods taught to him by Master Splinter. Because of his genius-IQ level, Donnie tends to over-analyze, overthink, and over-complicate things (especially Splinter's advice), ultimately putting too much of a burden on himself and making bad decisions.

Similarly, his social skills are slightly lacking. His nerdiness can sometimes get in the way of properly communicating and connecting with others.