Firefly, Ep. 1.07, “Jaynestown”
By far the most important thing about “Jaynestown”, the episode that finally gives Jayne the spotlight and a sheds light on at least one piece of his past, is that it doesn’t betray who Jayne is as a character. At this point each crew member aboard Serenity, with the possible exception of Shepherd Book, has been thoroughly fleshed out enough that they are fully realized people with histories, emotions, and opinions.