Macduff is a loyal Scottish nobleman and the Thane of Fife. After Macbeth murders Macduff's family, Macduff grieves for his loved ones and then resolves to kill Macbeth in man-to-man combat. At the play's end, he triumphantly carries Macbeth's severed head to Malcolm, the future king.
Macduff is not a man of many words, but he is one of the few characters in the play whose absence or silence speaks as much for him as his words. When Macduff speaks, you listen, because it's a rarity and because it's generally sensible and genuine. We first hear Macduff as he expresses honest grief at the King's murder, which he discovered. As we get to know Macduff, who is a strong and courageous soldier, we can appreciate how awful and deeply he felt Duncan's murder. It takes a lot to make this kind of man ramble on about his feelings. Macduff is additionally sharp and attentive; while everyone else panics and dithers about Duncan's death, Macduff is the one that asks why Macbeth killed the guards senselessly. He is also the first to see to the ailing Lady Macbeth, who cries for help upon hearing the news about the guards. Everyone else is too wrapped up in Macbeth's passion to do the practical thing and help the Lady. (Though, we should also note that Macduff mistakenly assumes that because Lady Macbeth is a woman, she's a fragile flower. He has no idea she played a big role in Duncan's death)
As the play unfolds, Macduff speaks with Ross about what's up, and there's no long "woe-be-unto man and Scotland" speeches. Instead of prattling on about his suspicions of the King, Macduff makes the quiet and powerful decision to just leave for England. This is not a cowardly act, but rather a brave one intended to aid Malcolm (who needs all the help he can get) in enlisting the English against Macbeth. It is clear from his talk with Malcolm that Macduff loves Scotland and is not willing to see her maligned by a new boss.
We truly discover the strength of Macduff's character when he meets with Ross and receives the terrible news of his family's murder. When Macduff hears of his loved ones' deaths, he is not afraid to express emotion and to grieve openly for his loss, despite Malcolm's insistence that he needs to be a "man" and get busy killing the guy responsible for his loss. This is a huge deal because Macduff is the only person in the play who insists that being a "man" means being able to "feel" things. Everybody else in Macbeth runs around insisting that masculinity is synonymous with violence and even cruelty. Not so, according to Macduff. Real men are able to express emotion.