The Wild Thornberrys is often regarded as one of the best Nicktoons of all time, but it's actually really messed up. Sure, the TV show has some great episodes, but Donnie's dark backstory definitely makes us do a double-take. How could this little boy be treated the way he is?
Though none of Nigel and Marianne's children have a normal life (they're busy being homeschooled, traveling the world, and talking to animals), Donnie has a particularly tragic experience. His life has been marked with loss and abandonment. When he's not busy trying to learn the English language on his own (he's picked up a few words despite never being educated), he's struggling to show his adoptive family his unique talents.
Donnie's horrible past is one of the bleakest Thornberry secrets. The adopted feral child is treated like an afterthought and is treated as such the moment his beloved orangutan surrogate mother gives him up. What Nickelodeon never explains is how the Thornberrys get away with their horrid mistreatment, how the village got away with it, and how the poachers who claimed Donnie's parents' life got away with it.
In The Origin of Donnie, the 2001 four-part TV movie that explains Donnie's strange beginnings, it's discovered that Donnie's parents are actually heroes. Michael and Lisa work with orangutans in Borneo while raising their young son. They love the primate species deeply and that affection ultimately leads to their death.
The animal-loving couple saves a pair of orangutans from a deathly trap. Poachers kill the couple afterwards as retribution and Donnie is tragically orphaned.
It's also discovered in The Origin of Donnie that Michael and Lisa's deaths come as a shock to more than just their beloved orangutans, as the couple's very well known in the Borneo village. Despite this, the villagers leave Donnie, a helpless babe, high and dry after his parents' murder.
They're perfectly okay with wild animals raising him; it's nonsensical, really.
Michael and Lisa's deaths are horrific and the orangutans that witness their end are touched by it (who said animals don't have feelings?). For this reason, the mother orangutan raises Donnie as her son.
He is fostered by these primates until Nigel and Marianne adopt him.
Donnie's orangutan mother loves him like an actual son, but she knows that he needs to be raised by his own kind. The scene in The Origin of Donnie when Nigel and Marianne welcome the feral boy to the Thornberry family is especially heartbreaking because the orangutan family must bid him goodbye.
His primate mom even cries as she watches her boy leave.