We know through Ace that the Redcap can reproduce with mortals and the resultant changelings would themselves be Redcaps should they choose Fae, but we haven’t seen any and he is referred to as The Redcap, denoting he is singular. Poor parenting perhaps if Ace is an example, none survived. This might suggest a relatively recent singular origin.

Personally, I never thought of Redcap as a separate species of Fae.  I believe the Redcap is just a fairly high ranking Sidhe, and his changeling offspring would just become a standard Sidhe.  I view the whole Redcap thing as an affectation of his.  He dips his hat in blood to terrify people, and goes by the name Redcap.  I know this doesn't jive with the real world mythology of Redcaps, but I think Jim just took some poetic license on that.

Thanks, been lurking for too long.  Decided to try to be a bit more active.  If you want to be really pedantic about it, you can pop Sue in either before or after Demonreach.  She roamed the earth about 67 million years ago. 

Sorry if this has been brought up before, but I've been trying to figure out who Bob's parents must be.  In an AMA Jim says "Both of Bob's parents have appeared in the Dresden Files. ".  I'm trying hard to figure out who they must be.  In Skin Game, Harry has this conversation with himself:

"She's a spiritual entity," I breathed. "Oh, my God. She's a spirit of intellect."
"What happens when mortals get it on with spirits," my double confirmed, though now without heat.

Assuming that's the only way for a spirit of intellect to be formed, that means that Bob's parents are a mortal and a spirit.  Bob's been around at least since the Middle Ages, since it was a Middle Age French wizard who bound him to the skull.  That should narrow down the suspect pool for the "mortal" parent.

I'm drawing a blank going further than this.  I would have gone with Lea as his mother, since he totally geeks out like a kid trying to get his parent's attention when he sees her.  Proximity to her would also give him a reason to have discovered the big bad secret of Halloween night, earning him a banishment with prejudice by Mab.  Lea is neither a spirit, nor mortal, though.

It's tough.  Perhaps it's Merlin and Demonreach.  Deliberately creating Bob, with the explicit purpose of being an instrument of translation for the Island in the future...  dunno.  Would explain how demonreach instantly knew how to interface with Bob.  *shrug*

Maybe there's no big reason or cool parentage at all.  Perhaps it was just Etienne the Enchanter and Ulsharavas.  No reason why he couldn't have had contact with the Oracle Spirit.

What are all your theories?