Assuming it isn't actually Mary, do you have any headcanons of what Vanderwood's first name is?
✿ I’ve always imagined when Vanderwood met Seven, their codename was just Vanderwood, and it was interactions with him that spawned the other bits.
‘Mary’ comes from an early conversation that Seven and Vanderwood had about the fictional people they admire. This is back when Seven was still really serious, so he’s rattling off all these famous computer science people and historical spies, and Vanderwood is like, ‘lmao Mary Poppins is my #1 hero’.
Seven is like… what? And Vanderwood sits him down, makes him watch that movie, and says look, not only does this woman have it together, she would make an excellent secret agent, tell me I’m wrong.
This actually gets a little laugh out of Seven, so Vanderwood - in an effort to make this horribly traumatized child laugh a little more - starts jokingly referring to themselves as ‘Mary Vanderwood’, and it…. sticks. To the point where they get a bit annoyed by it because it becomes a symbol of how Seven won’t take anything seriously, even the nature of their friendship (and if they’re even friends).
The ‘III’ bit is something Seven added, and it’s a bit of influence from V. V is sort of like… Seven’s replacement dad-slash-big-brother, right? And V came up with ‘Elizabeth the III’, so I could totally see Seven being influenced by that and appending it to Vanderwood’s name.
as for answering the actual question
I don’t have any specific headcanons in mind, other than Vanderwood probably doesn’t like being called by their birth name much. I’ve always imagined Vanderwood as being from England (since many of Seven’s jokes are actually true, and that’s one of the things he says about Vanderwood) so they’d have some sort of English name. lmao, maybe whenever they’re asked they say a different name, just to keep it mysterious.
maybe it’s something cool, like Ezekiel or Oswald