A redeemer is someone who delivers someone else from a problem by paying a price.

The concept is found in both Old and New Testaments.

In the Old Testament, the property of anyone in financial difficulties can be redeemed:

Leviticus 25 verse 25

25 “ ‘If your brother becomes poor, and sells some of his possessions, then his kinsman who is next to him shall come, and redeem that which his brother has sold.

Anyone who has sold himself to another can also be redeemed:

Leviticus 25 verses 47 - 49

47 “ ‘If an alien or temporary resident with you becomes rich, and your brother beside him has grown poor, and sells himself to the stranger or foreigner living amongst you, or to a member of the stranger’s family, 48 after he is sold he may be redeemed. One of his brothers may redeem him; 49 or his uncle, or his uncle’s son, may redeem him, or any who is a close relative to him of his family may redeem him; or if he has grown rich, he may redeem himself.

In the days of the judges, Boaz redeems the land that Naomi's husband sold and also agrees to marry Naomi's daughter-in-law:

Ruth 4 verses 3 - 5

3 He said to the near kinsman, “Naomi, who has come back out of the country of Moab, is selling the parcel of land, which was our brother Elimelech’s. 4 I thought I should tell you, saying, ‘Buy it before those who sit here, and before the elders of my people.’ If you will redeem it, redeem it; but if you will not redeem it, then tell me, that I may know. For there is no one to redeem it besides you; and I am after you.” 
He said, “I will redeem it.” 
5 Then Boaz said, “On the day you buy the field from the hand of Naomi, you must buy it also from Ruth the Moabitess, the wife of the dead, to raise up the name of the dead on his inheritance.” 

In the New Testament, the apostle Paul talks of us being delivered from the effects of sin by the sacrifice of Jesus Christ:

Romans 3 verse 24

24 being justified freely by his grace through the redemption that is in Christ Jesus;

Ephesians 1 verse 7

7 in whom we have our redemption through his blood, the forgiveness of our trespasses, according to the riches of his grace,