Hadley Correo is a time agent from the same future time period as JB. He is a jolly, and polite person. Based on how he interacts and jokes around with JB in the time cave, it is assumed that the two of them are friends. It is also hinted here that he has feelings for Angela DuPre.
In the epilogue of Redeemed, Hadley permanently moves to the twenty-first century to marry Angela and they adopt Maria Romanov and Leonid Sednev, as well as the unaged Gary and Hodge, who they rename 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 Two)
Caught (Book Three)
Revealed (Book Seven; Elucidator flashback only)
Redeemed (Book Eight)