Iago from William Shakespeare's Othello. He's been described as a "motiveless malignity". Indeed, the reasons he gives for manipulating everybody just aren't big enough for justification - in the end, it probably has to do with the fact that he finds it fun to control everyone and have them believe his every lie. He is among the greatest Magnificent Bastards is Theatre/Literature history.
William Shakespeare's Magnificent Bastardpar excellence is Richard III. Born with a slew of Red Right Hands and a truly twisted intellect, he takes to villainy, manipulation, and plans like a fish to water. He also possesses an unparalleled wit and charisma despite being deformed, managing to seduce the wife of a man he murdered over the man's corpse. He talks to the audience more than almost any other Shakespeare character, letting them in on his plans, and sharing his triumphs in wonderfully gloating asides. He's a vile and utterly self-centered man, but it's just about impossible not to admire how damn good he is at it. How much the real Richard III lived up to the "bastard" half of the equation is a matter of much controversy in historical circles.
Lady Macbeth is practically the whole driving force of the first half of the story, being the one who sets up the whole plot to kill King Duncan but in Act II she suffers Villainous Breakdown and is revealed to be more of a Smug Snake.
This play was basically Shakespeare's idea of putting an entire cast of magnificent bastards on one stage and watching them (literally) eat each other.
King Lear's Edmund. A bastard in every sense of the word, Edmund is an evil manipulator of the Iago variety, but he's also way cooler than his legitimate half brother Edgar, who, while not (particularly) stupid, is a total stiff. Edmund lies, forges, betrays, and seduces his way to the top, but part of you still can't help liking him. Especially since he actually says in a speech, "Stand up for bastards!" No apologies.
The Black Knight in Middleton's A GAME AT CHESS. When told "Your plot's discovered!" he smirks "Which of the twenty thousand and nine hundred/fourscore and five, canst tell?"
Harry Roat from Wait Until Dark, right from the very first scene when he traps Talman and Carlino into his plot.
Caldwell B. Cladwell, Corrupt Corporate Executive and Big Bad of Urinetown, most definitely qualifies. His bastardry is even more delicious when in the end it is revealed that as cruel as his methods were, they actually caused less harm to the people than when the heroes take over and make water consumption unlimited, resulting in an apocalyptic drought.
Few can compare with the Phantom from Webber's musical adaption of The Phantom of the Opera. He is a decidedly dark "Angel of Music" affected with a hint or two of madness, a hearty dollop of romantic obsession and a flair for dramatic trickery and murder. He's also a suave, half-masked genius who excels at seduction, manipulation, (possibly real) magic and arrogant bravado. Oh, and he manages to achieve most of this with some of the most potent male theatrical scores ever written. "Sing for me," indeed.
Petruchio from The Taming of the Shrew fits the bill. He manages to not only tame Katarina, but get two dowries. He tames Kate and successfully manipulates Baptista, Hortensio and Luciento, and a tailor.
Abigail Williams from The Crucible uses her intelligence, her sexual attractiveness, and her sense of humor to manipulate everyone around her, even arguably managing a Karma Houdini after essentially achieving mass murder.
Henrik Ibsen: Engstrand the carpenter from Ghosts. He is The Man Behind the Man, and the driving force behind the reverend Manders. He is instrumental in making Manders believe he himself was the one who set fire to the planned orphanage, and manipulates the reverend to put all the money from the Alving estate into a brothel he himself has planned, all without making the reverend suspicious. He only fails in securing his adopted daughter Regine for a "job" in his establishment.
Also Daniel Heire from The League Of Youth. He twirls the young hero of the play around his finger like nothing, makes him believe whatever he wants him to believe, and comes out of the play scott free, while the main character Stensgaard is put to shame.