[FredWolfLeonardo]

This is a legitimate question. The shows characters did have changes over time, but not in the same way as other tmnt shows since it was more episodic in nature. I'll try and give a list of what I remember, although there's probably more in the 193 episodes of the show that I've missed. Anyways, hee goes:

1. Leonardo started out very confident and gung go in season 1, but became more insecure and had a more innocent child like demeanor as the show went on. He would often boss the other turtles around alot to their annoyance and often be doubtful of his abilities as a leader (Leonardo Lightens Up, Take me to Your Leader). Over time however, he was more confident and effective as a leader which gave him the abilty to overcome his fears (Snakes Alive) and Overcome threats which were more dangerous then anything they had faced before (Dregg, Megavolt, The Glaxxons etc.)

2. Donatello started out as a character who loved inventions and used them for the benefit of his team, but doubted humanity for their unwillingless to help them with their battle against the forces of evil (beginning of Hot Rodding Teenagers from Dimension X). Slowly however, Donatello's doubts grew throughout the series, not only of humanity (Planet of the Turtleoids, Wrath of the Rat King etc.) but also of his own usefullness to the team (Donatello's Duplicate, Night of the Dark Turtle). Like Leonardo however, he later showed less signs of his weaknesses and became a more effective fighter.

Those are just two examples but there are plenty more for many characters I'll cite below:

1. The turtles become Ninja Masters by the final episode, a culmination of all of their training throughout the series.

2. Shredder and Krang started out as uneasy allies who would often argue and bicker, with Krang being the boss but they became more like equals as the series progressed, although they still were hostile towards each other alot. This changed in the Red Sky seasons when they were at their most vulnerable, so they became incredibly close, with Shredder even giving his life force (blood) to help save a dying Krang and saving him when he didn't need to.

3. Splinter started out as wanting to become human but in the season 1 finale, he let aside his desire in order to save the turtles from being de mutated by Shredder. However, he still wanted to be human deep down and his wish was granted in season 2 when Donatello was able to temporarily turn him back. Splinter however, saw that the human world had become selfish and uncaring, so in the end he permanently quenched his thirst for being human and was fully content with the life he had as a mutant rat. Splinter showed an embracing of his rat side in "Splinter Vanishes" when he was able to mind control the Rats far more effectively than the Rat King, an homage to how he started out in the sewers with the rats as his only friends.

4. Dregg started out as a calculating and intelligent Warlord who used intelligence and manipulation to try to conquer the earth and defeat the turtles. However, as the series went on and his defeats piled up, he became more brutal and starting more on the turtles rather than world domination. He eventually lost humanitys support at the end of season 9 and slowly become more crazy and obsessed, until finally snapping at the end and becoming a mindless monster. Its my personal favourite.

5. Baxter Stockman starts out as intelligent and bright, trying to sell his mousers. His invention is so effective however, that businesses rejected him. The Shredder did hire him, but treated him badly, leading to Baxter becoming more insecure and arrogant until it culminated into his betrayal of Shredder in "Curse of the Evil Eye". After that, their relationship only worsened as Shredder sent for Baxter to be killed by Krang in return for Bebop and Rocksteady. Instead of being killed however, Baxter became a mutant fly who then started become more feral minded as the series progressed. However, he gained a new friend in the form of a computer who was different from everyone else. Unlike Shredder and Krang, he didn't want anything out of Baxter other than for him to be happy.