Tom, also called Uncle Tom, is the protagonist of Uncle Tom's Cabin. He is a devout Christian man who believes in God's love regardless of earthly circumstances of sorrows or horrors. Even thou Tom's experiences later in the novel, after St. Clare's death, threaten to give his cause to doubt God's love, he stands firm and in the end dies a tragic death as a Christian.
Mr Haley is a slave trader. He is the reader who buys Tom from Harry and Mr. Shelby. Haley is a hypocrite who makes a public show of treating slaves well but in reality mistreats slavers with cruelty and violence.
St. Clare was murdered accidentally when he stopped at at tavern for the purpose of breaking up a brawl that had broken out there. St Clare had been talking and thinking the moral issues of freedom, slavery, abolition, emancipation and human dignity and rights and had decided to act like a just and concerned man, vowing to become involved in peoples lives by joining Abolition. In this frame of mind and with these ideals in his heart, he was out walking and came upon a bar-room brawl that he sought to put a peaceful stop to.
It was then that he was fatally stabbed and for the reason of being true to his new beliefs. It was a painful dramatic irony that St. Clare was killed while acting upon his new beliefs and resolves to help his fellow humankind, but it served the purpose of showing the spiritual safety and reward awaiting those who do as St. Clare did: believe rightly and act according to belief.