Library of the Dead - Glenn Cooper - Question!

Hello everyone! I've been wondering over this for the last few days.

I just finished the book "Library of the Dead" by Glenn Cooper, and i loved the book, but I'm still sitting back with a question!

When Dr. Atwood and his crew finds the Library in the first place, they also find a man who most certainly is not from the same age as the library. Most likely Elizabethan with J. C engraved on his pouch.

Who is this guy?

I'm wondering to death, if you know, please post it in the comment section below!

Thanks alot!