SPLINTER:
-Splinter is naturally in every Teenage Mutant Ninja Turtles continuity. He is their teacher and adoptive father, and continues to act as a wise old mentor figure throughout. His personality is usually calm, serene and considerate, making him almost as uniform in personality as the four Turtles. In nearly every continuity, Hamato Yoshi was in a relationship with Tang Shen, and both were attacked by a jealous Shredder. However, the ’80s toon removes this aspect entirely, and in many versions (including the original), Yoshi dies and Splinter is merely his pet rat, mutated into human form!

In the original Mirage Comics, Splinter is the pet rat of Yoshi, avenging him when he is killed. He is almost always an “at the base” character, and finally dies of a heart attack in a 2003 issue. However, it turns out that he’s alive in the Battle Nexus, and the one who died was a temporary imposter (really? They’re ripping off a 1960s X-Men twist?).

So in the ’80s toon, Splinter IS Hamato Yoshi, and was exiled from the Foot by Shredder’s underhanded tactics- he is later struck with Mutagen, turning him into a humanoid rat, and trains his four pet turtles in ninjitsu. Here, is is more of a teacher than a father. In Archie continuity, he was effectively the same as the 1980s Toon version, but once they stopped adapting cartoon episodes, he became a more active character, engaging in missions with his sons and even teaching April ninjitsu. The ’90s movies more or less copy the Mirage original, and are arguably the best at portraying a serene, loving father-figure, though this version appears to be the most crippled and weak, being more crafty and clever than good.

In the 2003 Cartoon, Splinter is now grey-furred, and keeps the Mirage origins, carrying a grudge against the Shredder for Yoshi’s murder. In the 2012 Nick Toon, he is more strict and serious than in other incarnations, but is the original Hamato Yoshi once more, having been mutated by the Kraang, along with his four songs. Tang Shen was killed in a fight against the jealous Oroku Saki, and Yoshi thought his daughter Miwa had died with her- it turns out in the big twist that his daughter survived, and was adopted by the Shredder as KARAI. This leads to several dramatic situations, as Karai has been trained to hate Yoshi. Splinter ultimately dies in battle with a mutated Super Shredder- his spirit appears before Leonardo and gives him the final Hero Point required to decapitate the Shredder, however.

In IDW Comics, he is established as being a reincarnation of the medieval-era Hamato Yoshi, who was murdered along with his four sons by Oroku Saki. Reincarnating as lab test subjects of Baxter Stockman’s, they are mutated and move on. He becomes obsessed with defeating the Shredder at one point, but ultimately beats him in an ancient challenge, and serves as Shredder’s second when he commits seppuku, slicing his head off. Shockingly, he accepted leadership of the Foot Clan from Karai, driving a wedge between him and his sons, even as he promises to make it more benevolent- they are horrified when he kills a foe or two, and ultimately he’s forced to walk back from this dark path. Finally, he sacrifices his life to bring Shredder back so that he can defeat an even greater enemy- he is reunited with Tang Shen in the afterlife.

In Rise of the TMNT, Splinter is a short, plump rat, and is now laid-back and very lazy, absent-minded, and forgetful. They change pretty much EVERYTHING about the guy, even more than the other characters, by turning him into a comic, mischievous prankster who was once a world-famous martial arts film star, but can suddenly get serious when the Shredder is involved.

-Splinter of course received a TV show version, in a pretty unchanged form- he’s still the Turtles’ stoic, calm, wise mentor figure. However, they made a significant change in his origin story- rather than being some rat that mimicked his master’s martial arts powers, he WAS the mutated Hamato Yoshi himself, making his battle with Oroku Saki much more personal. He’s not quite as… fatherly as his other versions have proved to be, and instead is often just “the guy who hangs out at the base”. Still, he has proven to be quite effective many times, and can outfight just about anybody (in one episode, he used the “Secret Technique That Only the True Leader of the Foot Clan Knows”, which consisted of Three Stooges movements and sound effects- it paralyzed Shredder and defeated him). When the four Turtles were captured during The Night of the Rogues, it was Splinter who gathered together a small group of humans that allowed them to rescue his sons and save the day.

His original toy kinda sucked, though- really shrimpy and with a fragile pink kimono that kinda got lost super-easily. Also he had a huge bow & arrow, along with other non-show-accurate weaponry. Though that kinda thing was pretty common with the early toys, who were released with “Weapon Sprues” that you had to take apart- giving you a lot of Shuriken, sticks and whatever those other blunt-ended two-pronged things were supposed to be.

Splinter is a remarkably bad-ass warrior when he fights- in most episodes when he does so, he defeats foes the other Turtles would struggle to fight. The notion of “he’s usually at home, but in a scrap he’s the mightiest” extends throughout nearly every continuity, so this build works for many variations of the character. Probably the toughest version, however, is in the 2012 Nick Toon, where he is so bad-ass he takes multiple minions and Foot Ninjas all at once, defeats the PL 11-tier Shredder more than once, and even beats the Super Shredder- it’s revealed that during the 4-on-1 sparring against his sons, he was ALWAYS holding back. They discover this to their horror when Splinter is mind-controlled into fighting them and DOESN’T restrain himself.

-The Splinter that’s more often seen in adaptations like the 2003 series & 2012 Nick Toon is generally a more stern, dominating figure, not afraid to teach tough lessons. He’s also much stronger, showing in episodes where he easily defeats all four Turtles combined, or takes down giants like Leatherhead laughably quickly.

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APRIL O’NEIL:
-As important to any Turtle to the franchise is their Human Buddy, and link to the “real world”, April O’Neil. Without her to act as a magnet for exposition, and of course a Damsel in Distress, you often don’t have a series at all. She is named after, and visually based on, Kevin Eastman’s first wife, April Fisher, which explains her Ambiguously Brown appearance in the Mirage books- her curly hair often makes her look black, but Fisher was of mixed race. The first cartoon turned her into a redhead, and this is the image that’s stuck in every other version until the VERY recent cartoon. Neither of the original creatures can agree on her ethnicity either (Peter Laird says she’s white), so this remains unclear. Initially Baxter Stockman’s lab assistant, she was shifted into a reporter, which again stuck for many other versions, though most recent versions of the tale have shifted that as well. In almost every continuity by the ’87 Toon, she is paired up romantically with Casey Jones as well- again, that toon remains a huge outlier in nearly every April story.

April was most typically a Damsel in Distress (nearly every video game features her- and sometimes Splinter- being captured by the Shredder), but most versions other than the ’97 Toon shift her into an increasingly-badass character, learning fighting from Splinter until she can sort of hold her own.

April’s a determined TV news journalist, always prepared for the late breaking news feature with her camcorder strapped ’round her arm. Her eagerness, however, gets her into trouble and makes her a big pain in the shell for the Turtles, who always end up saving the damsel in distress.

Still, April’s no air head and is a valuable member of the Turtle Team. Being a pretty human has its advantages, like getting into places the Turtles can’t. When the situation calls for more than a news flash, April’s ready with a trusty gun, which is secretly locked in her camcorder.
-From the toy description.

-The ’87 Toon’s version of April, which informed the Archie & Movie versions, shifted a HUGE amount of stuff about the character- she was again a victim saved by the TMNT, becoming their “Human Buddy” and link to the world outside the sewers, but nearly every aspect of her was changed, and most subsequent versions have scaled back a number of those changes, leaving this one a huge outlier. For startes, she was translated into a chesty redhead for the cartoon. And MAN was that something I glossed over when I was a kid- I was just all “Gee, she’s pretttyyyyyy…” when I was seven or whatever, but watching the show as an adult, I was like “!!! — I never noticed THAT!!” Head writer/creator David Wise based her signature hair and bright yellow jumpsuit off of Fujiko Mine’s garb in The Castle of Cagliostro, the famous Lupin III movie. April’s also 28 years old (much older than most “Human Buddy” characters, who tend to be teenagers, or sexy early-20s women), and acts ludicrously vain and image-centred. Almost like a parody of how young boys see women (the way Elliot on Scrubs is an exaggeration of how ADULT men see women).

April is also changed from a lab assistant to a TV reporter for “Channel 6”, usually running around with a hand-cam or something as she looks for a “hot scoop” or “The story of the CENTURY!”, thus necessitating her getting into even more trouble and having to be saved (this is probably WHY she was given that job, in fact). As she’s generally nosy and overly-curious, she gets kidnapped a LOT. Seriously, to a ridiculous, Lampshade-Hanging extent- it’s joked about within the series, within the fandom, and gets mentioned on Turtles Forever. “April Being Bound & Gagged” is practically a meme in the series, and it’s amazing I didn’t come out of my childhood with a Bondage Feti– hey, wait a second…

Notably, this is one of the only Aprils not to be paired off romantically with Casey Jones, nor become a badass fighter in her own right. “April Gets Mutated” was used as a plot device numerous times, with her becoming a cat-woman, fish-woman and giant wasp. In the latter-day “Red Sky” seasons, she leaves Channel 6 and works freelance for unknown reasons, and even distances herself from the boys, desiring to stop adventuring and get her life back on track.

April is a sub-optimal fighter, but a decent reporter & investigator, which kind of pays off when allied with the Turtles.

That shirt is a dead giveaway to the era, lol.

-The 2003 version of April was more like the Mirage villain in character, but kept the red hair, which had by this point become iconic. Wearing a very “2003” outfit consisting of a belly shirt and baggy khaki pants (like holy shit, this is the most dated aspect of the show now!), she is back as Baxter Stockman’s lab assistant and is now smarter and more capable. She also falls in love with her polar opposite- the slow-witted, brutish Casey Jones. April is a fairly decent fighter (enough to beat Mooks) and fairly smart in this version of the character.

-Now voiced by Katara & Tinker Bell’s VA, the Nick Toon version of April O’Neil is now the same age as the TMNT themselves, more of a sister than a “Team Mom”. A very young-looking, temperamental kid, she is crushed on by Donatello, loses her father to mutation, and more. She has some lower-grade Mental Powers as a result of the Kraang’s experiments on her mother, but my memory of the Nick toon has kind of faded.

OTHER APRILS:
-April differs wildly from version to version- the Mirage Comics version looks of mixed race at times, and marries Casey Jones. Shockingly, she turns out to be infertile… because she’s a LIVING DRAWING, her artist father magically “inking” her into existence. Okay that’s just weird. The Archie Comics version had exceptionally long hair and was the first version to become a fighter, wielding a katana at times. She was paired off romantically with the dragon-man Hothead.

RISE OF THE TMNT APRIL:
-This version of April is the first definitely-black April, now joining the hilariously-huge amount of red-haired characters who have been turned black in adaptations. I have no idea why it’s the redheads in particular, but HOLY HELL. Well, at least the earliest version is ambiguous so could be anything. This new design is arguably the most generic, as “Black Girl With Glasses & Twin Buns” is now an increasingly-common visual archetype for “Fun Sassy Smart Girl” to the point of becoming a cliche. SPEAING OF CLICHES, she is now the feisty, high-spirited and loud character, which goes into how THAT has become the new cliche for female characters in cartoons. It’s a recent modification of the “Smurfette Principal” where the One Chick who is boring and plain has shifted into being like Mabel Pine from Gravity Falls and sooooooooo many other female characters (Webby from DuckTales is a known recent one). Like, countering old standards of making the girl character boring and do-nothing, they’ve turned into loud nutjobs for LOLZ.

So um, in short, this character seems to be the most corporate-mandated, generic, thoughtless, “Well this is what’s popular, SOOOOO…” character in the damn cartoon. At least from reading the Wiki entry, so don’t quote me, lol. This April uses a magically-powered baseball bat and has a running gag where she has a new job every episode.