Vayeishev 1 - Chirah

38:1 - Yehudah leaves his brothers, and joins up with a guy from Adulam named Chirah.
38:12 - After the death of Yehudah's wife, the daughter of Shu'a, Yehudah is comforted, and goes up to Timnah to shear his sheep - he and Chirah, his Adulamite friend.
38:20 - Yehudah attempts to send a kid to Tamar as her payment through the agency of his Adulamite friend.

At first glance, Chirah seems to be a fairly unremarkable character. If this is the case, though, why does the Torah keep on pulling him into the story? And why does it tiptoe around his name so strangely? Do we see anyone else who's referred to by a moniker analogous to "his Adulamite friend"?

Chirah seems to be a positive character. When Yehudah sends him to find Tamar, he does not merely look on his own, but takes the initiative of asking around on his own if anyone was familiar with the prostitute who had been at the crossroads.

After the episode of Tamar and the birth of Peretz and Zerach, Chirah vanishes. When Yehudah is back with his brothers, we hear nothing more of this man, who was Yehudah's friend.

What's up with Chirah?