Elders were the first ones told, by Moses, about God's plan to free the children of Israel from Egyptian bondage (Exodus 3:16). The Old Testament elders asked the prophet Samuel to place a human king (instead of God) over all the people (1Samuel 8:5).
Old Testament elders could represent a city or town (Deuteronomy 19:12, 1Samuel 16:4), the people of a particular tribe (Numbers 22:7, Deuteronomy 31:28, 2Samuel 19:11), a family (2Samuel 12:17) or a country (Joshua 9:11). They were eligible to sit on the Sanhedrin, or properly the Great Sanhedrin, which met in Jerusalem and was the supreme council of the Jews.
The word translated as elder in the New Testament is the Greek word presbuteros (Strong's Concordance #G4245), which generally is used to refer to older men respected by others as leaders and role models. They were some of the most vehement adversaries against Jesus and his teachings.
It was known, in advance, that the elders would play a big part in causing the suffering and death of Jesus (Matthew 16:21, Mark 8:31, Luke 9:22). They, along with the chief priests and scribes, challenged Jesus' authority just days before the crucifixion (Matthew 21:23, Luke 20:1 - 2).
These men were among a group of leaders assembled at the High Priest's palace, just before the New Testament Passover, for the purpose of devising a way to have Jesus killed (Matthew 26:3 - 4).
The elders, along with the chief priests, bribed Judas with thirty pieces of silver in order to betray Jesus. When a sorrowful Judas gave the silver back them, they along with other leaders used it to buy a potter's field. This act fulfilled Bible prophecy (Matthew 26:14 - 16, 27:3 - 10).
It was the elders of Israel who also gave their authority, along with other Jewish leaders, to have Judas Iscariot escorted by armed men to the Garden of Gethsemane where Christ could be arrested (John 18:1 - 9, Matthew 26:47).
Additionally, it should be noted that it was the elders of Israel, along with the chief priests, who got a crowd of people to request a known murderer and robber named Barabbas be set free by the Romans instead of Jesus (Matthew 27:15 - 23).
The elders were among those who mocked Christ as he was dying on the cross (Matthew 27:41). They also played a crucial role in deciding, after Jesus' resurrection, to bribe Roman soldiers to lie about why his body was no longer in the Garden tomb (Matthew 28:11 - 15).
New Testament persecutors
Israel's elders, in the early days of the New Testament church, continued their opposition to Jesus by taking every opportunity to destroy those who believed in him. They, along with the High Priest and others, were furious that Peter and John were preaching the gospel to the masses. Peter and John, after being questioned as to why they are preaching Jesus and by what power a lame man was healed, were released (Acts 3:1 - 10, 4:5 - 6, 23).
They, with the chief priests, also conspired with more than forty other Jews to have the apostle Paul murdered (Acts 23:12 - 15). They were willing to make the long trip from Jerusalem to Caesarea in order to, before the Romans, testify against the apostle Paul and what he taught (Acts 24:1).