Final answer:
Charles Sumner was the Senator from Massachusetts and a prominent Radical in Congress. He advocated for integrating schools and giving Black men the right to vote while disenfranchising many southern voters.
Step-by-step explanation:
The Senator from Massachusetts and a prominent Radical in Congress was Charles Sumner. He was a leading Radical Republican in Congress who advocated for integrating schools and giving Black men the right to vote while disenfranchising many southern voters. Sumner believed that when the southern states seceded, they committed "state self-destruction" and had to apply for readmission to the Union, with only Congress having the right to set the terms.