John the Baptist taking a stand against King Herod's sin.
But when Herod heard thereof, he said, It is John, whom I beheaded: he is risen from the dead. For Herod himself had sent forth and laid hold upon John, and bound him in prison for Herodias' sake, his brother Philip's wife: for he had married her. For John had said unto Herod, It is not lawful for thee to have thy brother's wife. Therefore Herodias had a quarrel against him, and would have killed him; but she could not: For Herod feared John, knowing that he was a just man and an holy, and observed him; and when he heard him, he did many things, and heard him gladly. And when a convenient day was come, that Herod on his birthday made a supper to his lords, high captains, and chief estates of Galilee; And when the daughter of the said Herodias came in, and danced, and pleased Herod and them that sat with him, the king said unto the damsel, Ask of me whatsoever thou wilt, and I will give it thee. And he sware unto her, Whatsoever thou shalt ask of me, I will give it thee, unto the half of my kingdom. And she went forth, and said unto her mother, What shall I ask? And she said, The head of John the Baptist. And she came in straightway with haste unto the king, and asked, saying, I will that thou give me by and by in a charger the head of John the Baptist. And the king was exceeding sorry; yet for his oath's sake, and for their sakes which sat with him, he would not reject her. (Mark 6:16-26)
Esther risking her life before the King:
And Esther spake yet again before the king, and fell down at his feet, and besought him with tears to put away the mischief of Haman the Agagite, and his device that he had devised against the Jews. (Est_8:3)
Samuel, uncovering the King's sin:
And there came a traveller unto the rich man, and he spared to take of his own flock and of his own herd, to dress for the wayfaring man that was come unto him; but took the poor man's lamb, and dressed it for the man that was come to him. And David's anger was greatly kindled against the man; and he said to Nathan, As the LORD liveth, the man that hath done this thing shall surely die: And he shall restore the lamb fourfold, because he did this thing, and because he had no pity. And Nathan said to David, Thou art the man. Thus saith the LORD God of Israel, I anointed thee king over Israel, and I delivered thee out of the hand of Saul; (2 Sam 12:4-7)
John the Baptist was a public act of conscience, but the other two were private.