Days of our Lives: when did Chad Peterson-Woods become a regular character?

Obviously Mia is gone: IDK why & don't really care but she DID just kinda disappear did she not? I never liked Chad but now it looks like he may be a reg. character w his dad being the D.A. & his mother a judge. There is definitely something about Madeleine we don't know. My theory is she doesn't want her past (as a call girl like Kate) to come out now that she's a judge & maybe Kate is afraid she may have something on her. Anyway why is Chad even here? I don't like him at all. Also NO explanation to where Mia went? Not that I care like I said lol.