The prophecy reads (KJV):
Benjamin shall ravin as a wolf: in the morning he shall devour the prey, and at night he shall divide the spoil. (Genesis 49:27)
What does this mean, and was it fulfilled?
Jacob's prophecy about Benjamin as a ravenous wolf may refer to the tribe's collective greediness as well as its prowess as warriors. "Dividing the spoils" may be a reference to the Benjamite Saul's action of despoiling the Amalekites, against the instruction of the prophet Samuel. Or it may be a reference to the tribe of Benjamin being given hundreds of young women by the other tribes of Israel after Israel wiped out the men of Jabesh-Gilead in Judges 21.
After the Israelites defeated the Benjamites in an almost-genocidal civil war, (Judges 19-21) the men of Israel decided to have compassion on their former enemies:
“Go and smite the inhabitants of Ja′besh-gil′ead with the edge of the sword; also the women and the little ones. This is what you shall do; every male and every woman that has lain with a male you shall utterly destroy.” And they found among the inhabitants of Ja′besh-gil′ead four hundred young virgins who had not known man by lying with him; and they brought them to the camp at Shiloh, which is in the land of Canaan... And Benjamin returned at that time; and they gave them the women whom they had saved alive of the women of Ja′besh-gil′ead.
Here the virgin women are spoils of war, given to the Benjamites in order to save them from extinction. Although, from the standpoint of Israel, the Benjamites collectively had acted as ravenous wolves by raping the Levite's concubine (Judges 19), here they were allowed to "divide the spoils" of Israel's war.
Samuel said to Saul... "Now go and smite Am′alek, and utterly destroy all that they have; do not spare them, but kill both man and woman, infant and suckling, ox and sheep, camel and ass." ...Saul defeated the Amal′ekites, from Hav′ilah as far as Shur, which is east of Egypt. 8 And he took Agag the king of the Amal′ekites alive, and utterly destroyed all the people with the edge of the sword. 9 But Saul and the people spared Agag, and the best of the sheep and of the oxen and of the fatlings, and the lambs, and all that was good, and would not utterly destroy them; all that was despised and worthless they utterly destroyed. (1 Sam. 15)
Here, the prophetic reference to devouring the prey in the morning and dividing the spoil at night (also translated as evening) may be interpreted as referring to the Benjamite Saul slaughtering the Amalekites during the day and despoiling them after the battle.
Earlier, the tribe of Benjamin earned a reputation as strong warriors. During the Exodus, Benjamin camped with the two tribes of Joseph and mustered tens of thousands of men (Num. 1:36, 10:22-24; 24:41; 1 Chron. 7:6-11). Some of them drilled as left-handed fighters and many were ambidextrous (Judges 20:16, 1 Chron. 12:12). They were known as brave and skilled archers (I Chron. 7:40, II Chron. 14:7).
During the time of the judges, a small number of Benjamites living in Gibeah infamously raped a Levite's concubine, bringing the whole tribe under a ban, followed by a civil war in which the tribe was nearly wiped out. After surviving this fate, the Benjamite, a highly successful war leader himself, became Israel's first king. After his death, his son Ish-bosheth, reigned for several years over the northern tribes in the time of King David. Psalm 68 refers to Benjamin's leadership:
God will shatter the heads of his enemies,
the hairy crown of him who walks in his guilty ways...
Thy solemn processions are seen, O God,
the processions of my God, my King, into the sanctuary...
There is Benjamin, the least of them, in the lead,
the princes of Judah in their throng,
the princes of Zeb′ulun, the princes of Naph′tali.
As a side note, we should also be aware of the prophecy of Moses in Deut. 33:
Of Benjamin he said,
“The beloved of the Lord,
he dwells in safety by him;
he encompasses him all the day long,
and makes his dwelling between his shoulders.”
This probably refers to Benjamin's later status as an adopted member of the nation of Judah. In this context we may also think of the identity of the Apostle Paul as a Benjamite. (Philippians 3:5)
Conclusion: about the OP's question about the meaning of "ravenous wolf" and "dividing the spoil" there are two likely possibilities. It may refer to Benjamin's being given hundreds of young women as war booty after Israel's extermination of the other people of Jabesh-Gilead. This came after Benjamin was held collectively responsible for its members, acting as "ravenous wolves," raping the Levite's concubine. The prophecy may also refer to the Benjamite Saul's defeat of the Amalekites. Once he defeated them earlier in the day, he despoiled them (in the evening), contradicting the instruction of the prophet Samuel.
“Ravin” is an archaic form of “raven,” where we get the more common “ravenous”; thus to “ravin as a wolf” would mean to consume greedily and fiercely, as a wild wolf. This translation of טָרַף or taraph (glossed “to tear, rend, pluck”) seems apt enough: Jacob doubtless uses an idiom that, literally, means Benjamin is a wolf (זְאֵב or zeeb) that tears; but the implication is that his descendants will be a violent mob that consumes whatever they can get their hands on.
This well describes the infamous and monstrous behavior, in Judg 19:22-27 and 20:21, 25, that will bring on their decimation in 20:34-48. I will not retell this story, which is one of the darkest in the entire Bible, except in summary: some Benjamites rape the concubine-wife of a Levite to death; he sends her in pieces to the Israelites to call them to do justice; the Benjamites kill tens of thousands of Israelites when they come to mete out justice; and finally the Benjamites are themselves slaughtered and reduced to just 600 men.
As to “at night he shall divide the spoil”, it is a bit shocking, I think, to reflect that this somewhat describes the fate of the Levite’s concubine: a mob of Benjamites raped, or despoiled, her to the point of death at night, and in the morning the Levite divided her corpse into twelve parts and sent it to the twelve tribes: “And when he was come into his house, he took a knife, and laid hold on his concubine, and divided her, together with her bones, into twelve pieces, and sent her into all the coasts of Israel.” (Judg 19:29)
The aptness of this act as a fulfillment of the prophecy, and the difficulty in explaining the shocking act of dismemberment otherwise, suggests that the Levite bore in mind this prophecy about Benjamin, and that he quite deliberately made the fulfillment of “divide the spoil” literal. This is, of course, just a hypothesis, and I would be curious to know if scholars had discussed it.