Hadley Correo is a time traveller from the same time period as JB. He is a jolly, and polite person. It is assumed that he is a friend of JB's from the book Sent. As well he has some relationship with Angela DuPre.
At the end of Redeemed, Hadley married Angela and they adopt Maria Romanov and the servant boy from 1918 Russia, and baby Gary and Hodge, who they call Gregory and Henry.
According to Jonah in Sent Hadley is said to be "an old, whiskery man" (page 264 in Sent). In Caught he is said to have jolly eyes with a twinkle in them.
JB - Friend; fellow time travel worker
Angela - Romantic interest (said to be "special friends" in Caught)
Sent (Book 2)
Caught (Book 5)
Redeemed (Book 8)