She (Leah) conceived again, and when she gave birth to a son she said, "Because the LORD heard that I am not loved, he gave me this one too." So she named him Simeon. (Genesis 29:33)
The second son of Jacob by Leah, Simeon's loyalty to his family was opportunistic. This was evidenced by the fact that he joined with his brothers in selling their brother Joseph to the Ishmaelites. For that he was temporarily held as a hostage after Joseph's rise to power in Egypt.
Simeon was with Levi in the terrible act of vengeance against Hamor and the Shechemites. This was in revenge for Hamor defiling their sister Dinah, even though Hamor said he would marry Dinah and had fulfulled their precondition to be circumcized. By a strange subterfuge all the Shechemites were rendered helpless and slaughtered by the two irate brothers who then, together with the other sons of the patriarch, plundered the city.
All the men who went out of the city gate agreed with Hamor and his son Shechem, and every male in the city was circumcised. Three days later, while all of them were still in pain, two of Jacob's sons, Simeon and Levi, Dinah's brothers, took their swords and attacked the unsuspecting city, killing every male. They put Hamor and his son Shechem to the sword and took Dinah from Shechem's house and left. (Genesis 34:24-26)
This later brought on the malediction of a dying father.
"Simeon and Levi are brothers-
their swords are weapons of violence.
Let me not enter their council,
let me not join their assembly,
for they have killed men in their anger
and hamstrung oxen as they pleased.
Cursed be their anger, so fierce,
and their fury, so cruel!
I will scatter them in Jacob
and disperse them in Israel.
After the Israelites crossed the Jordan into the Promised Land, the offspring of Simeon, the tribe of Simeon, were allotted the territory in the south of the land promised to the descendants of Abraham, Isaac and Jacob, which included the cities of Beersheba and Arad. The tribe of Simeon eventually unified into the tribe of Judah.