Monostatos is something of an anomaly in the opera The Magic Flute. He seems a strange character to have fetched up in Sarastro's temple and why on earth Sarastro puts him in charge of Pamina in the first place has always seemed inexplicable to me. No explanation is supplied for this act in the story.
Monostatos is a combination of the opposite of Tamino and Papageno. Like Papageno, he is seen as unusual in that he is a Moor and is often portrayed as a black person. In many productions though not all a white singer will play the part with his face blacked to enhance this part of the role.
Monostatos first appears in Sarastro's temple supposedly guarding Pamina. However his lust for Pamina is such that she desperately tries to escape from his tormenting and eventually succeeds when Papageno appears. Papageno and Monostatos encounter one another after Pamina has fainted, and both are afraid of the other's difference (neither has seen anything like the other before) and run away from one another. Monostatos finally attempts to recapture Papageno and Pamina when they are trying to make their way back to Tamino, but Papageno uses the Magic Bells and the Bells' enchantment saves them. He eventually captures Tamino instead and brings him before Sarastro.
In the final part of Act 1 of the opera, Pamina tells Sarastro why she has tried to escape, and Sarastro rewards Monostatos for his deeds by telling his slaves not to give him more than 77 strokes of the bastinado. This unpleasant punishment is Monostatos' undoing as he begins to revolt against Sarastro.
In Act 2 of the opera Monostatos' next appearance is when he creeps up to Pamina's whilst she is sleeping and once again his lust overcomes him. The Queen of the Night appears at the crucial moment but following her order to Pamina to kill Sarastro, Monostatos then tries to blackmail Pamina. Sarastro comes in having overheard this and dismisses him. Monostatos is seen for the last time when the Queen of the Night and her ladies attempt to storm the temple. The Queen has promised him Pamina after the temple is captured but of course they fail.
The role of Monostatos is usually sung by a baritone with a fairly light voice. His music has its own style unlike that of any other character in the opera, especially as Monostatos' role with both sides is unlike that of the other characters.
Monostatos has five appearances within the opera (it has been suggested by a number of authors that this might relate to the fact that the number 5 is representative of a woman in Masonic ritual) and has a number of pieces to sing.
His first appearance is a duet with Pamina (Der Tod macht mich nicht heben/He/Sklaven, legt ihr Fesseln an) followed almost immediately by the duet "hu - - des ist - der Teufel sicherlich". Then he interrupts Pamina and Papageno's "nur geschwinde" with his short aria "nur geschwinde, nur geschwinde" and the chorus that the slaves sing when the bells enchant them "Das klinget so herrlich".
He has some recitative in the scene with Sarastro, Tamino, Pamina, Papageno and the chorus at the end of Act 1 and then his next aria is the menacing "Alles fuhlt der Liebe Freuden" when he creeps up to the sleeping Pamina. His final appearance is in the chorus and dialogue at the end with the Queen of the Night and the Three Ladies (notice again the number five also here).
Monostatos is not the most pleasant of characters in The Magic Flute and the role requires both a good actor and a fine singer to bring it out at its best. The role is not really a comic one although parts of it (for example when Monostatos and Papageno run away from one another) are often portrayed as such. He does have some fine music to sing and the role is well worth studying as part of your overall knowledge of the opera.