Hen Wen was a white pig owned by Coll Son of Collfrewr, who lived at Caer Dallben in the south of Prydain. By "white" it remains unknown whether author Lloyd Alexander meant literally bone-white, or as a euphemism for "pink".
Hen Wen looked and behaved like a normal sow, yet she was oracular, possessing the ability to tell the future and reveal hidden information. Dallben used a set of Letter Sticks -- rods of ash wood with letters and symbols carved on them -- to help Hen communicate her visions, by pointing at letters with her snout. The prophetic messages she generated were cryptic and terse; Hen Wen herself seemed to fear the very sight of the Letter Sticks, as though the task were somehow onerous.
For a pig Hen lived a fairly dangerous life. Arawn himself once dispatched his Huntsmen of Annuvin to capture and bring her to Annuvin, from which she was rescued, with the help of a few animals, by Coll Son of Collfrewr.
Taran took over the primary responsibility for Hen Wen's care, which led to Coll dubbing him "Assistant Pig-Keeper." Hen fled Caer Dallben when the Horned King drew near the farm; Gwydion, too, had journeyed there to glean answers from Hen; north of the farm he met Taran, who helped him search for the missing pig. Despite Gurgi's spotting her on the banks of the Great Avren river, Hen vanished without a trace. As it happened, the Fair Folk had nabbed her almost under Gwydion and Taran's noses, and taken her to their hidden kingdom for safe keeping. When Taran and the Companions were detained by King Eiddileg under The Black Lake, Gurgi found her in good condition, and she was reunited with Taran. Near Caer Dathyl, however, she slipped away from him once more, running to tell Gwydion the Horned King's secret name, which gave the Prince of Don power over the evil warlord, and allowed him to defeat Arawn's champion.
Hen appeared briefly in The Black Cauldron and Taran Wanderer. In the former she was receiving a bath from Taran when Prince Ellidyr arrived, barking orders at the "pig boy". In the latter, when Taran asked her if she could tell him of his parentage (owing to her deep knowledge) she replied only in her customary grunts and wheezes.
Hen's prophesies using the Letter Sticks imparted some clues as to the events to come, particularly with regard to the fate of Dyrnwyn. Hen Wen herself was terrified by what the visions showed her, and the ashwood rods were destroyed in the effort of her final prophecy.
Taran's war banner -- the banner of the White Pig -- had begun as a piece of embroidery accomplished by Princess Eilonwy during her studies on the Isle of Mona. For Taran's sake, the men of the Free Commots rallied under the banner; later, on the war path to Caer Dathyl, it served as a warning -- after several victories against marauders -- that those riding under the banner of the White Pig were not to be harassed.
After enchantment passed out of Prydain, Hen became an ordinary sow -- and, it is suggested, a happier one. Taran was overjoyed that she was able to remain behind with him in Prydain, now the dam of several squealing piglets.
Hen Wen is essentially the same in the 1985 animated film, but she's pink instead of white, and smaller than a normal pig. She also seems to have more human-like intelligence, though that may a product of the Dinseyfication of the material in general.
In the movie the Letter Sticks are replaced by a bowl of enchanted liquid, which when Hen touches her snout to the surface reveals visions of what's to come. This power can also be used to watch (scry) concurrent events.
The "old white" sow Henwen appears in the Welsh Triads, specifically in the Red Book of Hergest (Welsh: Llyfr Coch Hergest), a large vellum manuscript written shortly after 1382. Under the section titled "These Are the Triads of the Horses" is a subsection:
- Three Powerful Swineherds of the Island of Britain:
- And the third, Coll son of Collfrewy, tending the swine of Dallwyr Dallben in Glyn Dallwyr in Cornwall. And one of the swine was pregnant, Henwen was her name. And it was prophecied that the Island of Britain would be the worse for the womb-burden. Then Arthur assembled the army of the Island of Britain, and set out to seek to destroy her. And then she set off, about to bring forth (?), and at Penrhyn Awstin in Cornwall she entered the sea, and the Powerful Swineherd after her. And in the Wheat Field in Gwent she brought forth a grain of wheat and a bee. And therefore from that day to this the Wheat Field in Gwent is the best place for wheat and for bees. And at Llonion in Pembroke she brought forth a grain of barley and a grain of wheat. Therefore, the barley of Llonion is proverbial. At the Hill of Cyferthwch in Arfon she brought forth a (wolf-cub) and a young eagle. The wolf was given to (M)ergaed and the eagle to Breat, a prince of the North: and they were both the worse for them. And at Llanfair in Arfon under the Black Rock she brought forth a kitten, and the Powerful Swineherd threw it from the Rock into the sea. And the sons of Palug fostered it in Môn, to their own harm: and that was Palug's Cat, and it was one of the Three Great Oppressions of Môn, nurtured therein.
The Triads in Peniarth MS 54 offer a slightly different account, wherein "the ancient sow" is not named:
- 23. Three powerful swineherds of the Isla[n]d of Prydain. [The first two are listed.] And Coll son of Collfrewy, who kept the ancient sow of Dallweir Dalben, who went burrowing as far as Penryn Awstin in Cornwall, and there going to the sea, landed at Abertorogi in Gwent Iscoed, and Coll son of Collfrewy having his hand on her bristles, wherever she went on the sea or on the land, and at Maes Gwenith in Gwent she dropped wheat and bees, and from henceforth there is the best wheat there, and from thence she went to Lonwen in Penbro, and there she dropped barley and bees, and from thence there is the best barley in Lonwen, and from thence she proceeded to the Riw Cyferthwch in Eryri, and there she dropped a wolf-cub and an eagle, and Coll son of Collfreuy gave the eagle to Brynach Gwyddel of the north, and the wolf he gave to Menwaed fo Arllechwedd, and these are the wolf of Menwaed and the eagle of Brynach, and thence going to Maendu in Llanfare, in Arvon, and there she dropped a kitten, and Coll son of Collfrewy threw the kitten in the Menai, and she became afterwards the Paluc cat.