This episode of Um, Actually, the college humor quiz show about correcting fandom trivia, gives the name of Tobias from Animorphs as "Tobias Santorelli". This is not the thing intended to be corrected, that's some other nonsense; they apparently thought that was his real name when writing the question.

Problem: we mostly don't know the Animorphs' last names. We know Jake's (Berenson), and we have strong reasons to expect Rachel's is the same (they're cousins and their fathers are brothers), and of course Ax's full name is never secret, but we don't know for Cassie, Marco, and Tobias.

(Some people think Tobias' last name is Fangor. It's an understandable mistake, that was the legal name of his ~biological father, but Tobias doesn't have the name of his biological father but rather that of the man his mother married afterwards, who is not known)

I looked it up, and found a handful of websites mentioning "Tobias Sirinial Santorelli" as his full name. I know why Sirinial, but where the fuck do they get Santorelli from? Seerowpedia reminds me there is in fact a character named Santorelli in canon, he is a super minor guy who shows up only in the last book.

So I'm thinking, did someone make up a fanon name for Tobias that somehow spread? Who? Why? And then I find this, and I know exactly who and why.

That is a wiki for Neomorphs, a post-canon fanfic that continues the plot of Animorphs past book 54. In it, minor character Santorelli gets developed a bunch and among other things, retroactively becomes Tobias' stepfather via time travel shenanigans (time travel shenanigans are a major aspect of Animorphs). So, in that fic, his surname actually is Santorelli.

Here's the fun part: I had already read Neomorphs, many years ago, back when I was active in the fandom. I know the guy who wrote it, we were in the same forum. I think at one point I did beta reading for his original fiction. All this knowledge was in fact hidden somewhere deep inside my brain, but I could not unlock it.

And somehow it went from a fanfic name to a fanon name to someone mistaking it for a canon name when writing questions for a fandom trivia quiz youtube show.

bonus: chat log record of me realising all this in real time: