Amalek

Amalek was a nation in the Torah and Old Testament whose people called the Amalekites were enemies of the Israelites.
Genesis.
In the Book of Genesis, Chapter 36 Verse 10, Esau married a woman named Ada and she gave birth to a son named Eliphaz. Then in Chapter 36 Verse 12, Eliphaz had a concubine named Timna and she gave birth to a son named Amalek.
Exodus.
In the Book of Exodus Chapter 17, Amalek’s descendants called the Amalekites attacked the Israelites after the Israelites left Egypt. So Moses sent Joshua to fight the Amalekites. As long as Moses held his hands in the air, the Israelites were winning but Moses’s hands got tired so he got his brother Aaron to hold one up while Hur held the other up. And Joshua beat the Amalekites. 
Then in the Book of Exodus Chapter 17 Verse 14, the Lord told Moses “write this for a memorial in the book and recount it in the hearing of Joshua, that I will utterly blot out the name of Amalek from under heaven”.
Numbers.
In the Book of Numbers, King Balak of Moab hired Balaam to curse the Israelites but Balaam ended up blessing the Israelites instead. And when Balaam had a vision of the future of the Israelites and their victory over their enemies, he said “ Amalek was the first of the nations but his end shall come to destruction” (Numbers 24:20).
Deuteronomy.
In the Book of Deuteronomy, Chapter 25, the Lord tells the Israelites to “remember what Amalek did to you on the way as you were coming out of Egypt” that the Amalekites attacked the Israelites from behind and killed the tired and weak. And because of it, the Lord tells the Israelites to “blot out the remembrance of Amalek from beneath heaven. You shall not forget.” 
First Samuel.
In the first Book of Samuel, Chapter 15, the Lord told Samuel to tell Saul to kill all Amalekites and destroy all of their property and kill all their animals because it was something that the Lord told the Israelites to do back in the time of Moses. But when Saul attacked Amalek, he captured King Agag instead of killing him and Saul and his warriors kept the best animals for themselves but “everything despised and worthless that they utterly destroyed” (1 Samuel 15:9). So the Lord sent Samuel to King Saul to tell him “now the Lord sent you on a mission and said “go and utterly destroy the sinners, the Amalekites, and fight against them until they are exterminated. Why then did you not obey the voice of the Lord?”. (1 Samuel 15:18-19). When Saul said that he killed the Amalekites except for their king and was actually going to sacrifice their animals to the Lord, Samuel told him
“Has the Lord as great delight in burnt offerings and sacrifices as in obeying the voice of the Lord. Behold to obey is better than sacrifice and to heed than the fat of rams. For rebellion is as the sin of witchcraft and stubbornness is as iniquity and idolatry. Because you have rejected the word of the Lord, He has also rejected you from being king.” 
Then Samuel told Saul to bring the Amalekite King Agag to him and Saul did. And Saul told Agag “As your sword has made women childless so shall your mother be childless among women” and cut Agag to pieces. (1 Samuel 15:33)
Later on in the first of the Books of Samuel, David fights the Amalekites.
Second Samuel.
In the second book of Samuel, a man told David that he is the son of an Amalekite and that he happened to be on Mount Gilboa after the battle. The man said that Saul asked him who he was and he told him “an Amalekite”. The Amalekite said that Saul asked him to kill him so that the Philistines couldn’t torture him and he killed Saul. David said the man was a murderer because he killed the King of Israel so David cut his head off. 
Chronicles.
In the Books of Chronicles, there is a family tree which says that Esau became the father of Eliphaz and Eliphaz became the father of Amalek.