Gamaliel was the Pharisee and respected teacher of the law who advised the Sanhedrin to leave the apostles alone.
The episode appears in Acts 5. After the apostles were arrested for preaching about Jesus, the council considered harsher action. Gamaliel stood up, ordered the apostles removed briefly, and warned the council not to act rashly. His argument was that movements created by human beings would fail, whereas a work from God could not be stopped.
Acts identifies him as a Pharisee and a teacher of the law held in high regard. His counsel persuaded the council not to execute the apostles, although they still had them flogged and ordered them not to preach in Jesus’ name. The apostles then continued teaching.
This Gamaliel is generally identified with Rabban Gamaliel the Elder, a leading first-century Jewish authority and grandson of Hillel the Elder. Acts also records Paul saying that he had been educated under Gamaliel, but that detail should not be confused with Gamaliel II, a later rabbinic leader.