King Duncan was. Macbeth killed him and then he was crowned King!
If you mean the character in Shakespeare's play, then this is what he did: He listened to the witches, killed Duncan the king of Scotland, then created a rebelion against him where Macbeth and Macduff fight to the death and Macbeth gets killed by Macduff, making Macduff's son Michael the king of Scotland.
Robert Bruce was crowned twice, the first time by Bishop Robert Wishart; and again the following day by Isabella MacDuff as it was a tradition since the death of King Macbeth that the king of Scotland be coronated by a MacDuff.
Macduff is trying to defeat Macbeth and overthrow him as king of Scotland. He is motivated by his desire to avenge the murder of his family, which was ordered by Macbeth. Macduff's ultimate goal is to restore peace and order to Scotland by removing Macbeth from power.
Macbeth kills Duncan, the King of Scotland, to take the throne. Malcolm, Duncan's son, eventually defeats Macbeth and becomes the rightful king, declaring Scotland free from Macbeth's tyrannical rule.
Macduff is in England during Act 3. He has gone there to seek help from King Edward of England to overthrow Macbeth and restore rightful rule to Scotland.
Malcom is Duncan's son. Macbeth kills Duncan (king of Scotland), but not Malcom; Malcom flees to escape suspicion of his involvement in his father's murder. He later returns to Scotland, where, after Macduff kills Macbeth, he is crowned king. Hope this helps!
A number of people including Macduff and Ross.
Malcolm, son of King Duncan, was crowned King of Scotland after Macbeth's death. He was able to reclaim the throne with the help of his ally, Macduff.
After he crosses the brink of insanity, Macduff and Malcolm lead forces to retake the throne. In a battle, Macduff kills Macbeth and delivers his head to the new king, Malcolm, who then begins the Tudor-esque age in Scotland (making the Thanes into Earls)
Macbeth is first 'Thane of Glamis' then he is bestowed the title 'Thane of Cawdor' then king of Scotland
Macduff was a noble Scotsman. Duncan I [d. August 14, 1040] was the King of Scotland. Therefore, Macduff knew who King Duncan was. He was the King's subject. Additionally, Macduff appeared to number among those noble Scotsmen upon whom the King counted and with whom he moved most closely. Specifically, Macduff was the nobleman whom the King had asked to make sure that he was up and moving on to the next stop after the Macbeths' castle at Inverness. Macduff didn't get to carry out that task, because the King and his two royal guards were stabbed to death the night before.
Malcolm reveals his flaws to Macduff in order to test his loyalty and see if he truly has Scotland's best interests at heart. By pretending to be a worse candidate for king than he actually is, Malcolm is able to gauge Macduff's reaction and trustworthiness.