King Lear is full of deception and there is plenty in Act One.
The first instances of deception occur in the first scene of the first act. Lear intends to divide his kingdom amongst his three daughters and will give the greatest portion to the daughter who professes the most love for him. Cordelia is the only daughter who speaks plainly and honestly. Goneril and Regan deceive everyone (except Kent and Cordelia) with their effusive professions of love for the king. Cordelia points out that her sisters' speeches are full of superficial praise and reasons with Lear to reconsider, but he does not. Finally, she warns her sisters that their lies will be discovered but hopes they will live up to their praise of the king:
Time shall unfold what plaited cunning hides:
Who covers faults, at last shame them derides.
Well may you prosper! (I.i.308-10)
Soon to follow, more deception occurs in the very next scene. In the subplot of the play, Edmund conspires to get land and the title of Earl of Gloucester from his brother Edgar, who is the legitimate heir. Edmund forges a letter in Edgar's name which claims that Edgar plans to murder his father, the Earl of Gloucester. Edmund also deceives his brother into thinking he has his best interests in mind. Edmund informs Edgar that his father is not pleased with him. Edgar rightly assumes that he is being framed. Edmund responds:
That's my fear. I pray you, have a continent forebearance, / till the speed of his rage goes slower; and as I say, retire with / me to my lodging from whence I will fitly bring you to hear, / my lord speak; pray ye, go; there's my key: if you do stir / abroad, go armed. (I.ii.159-63)
Act One, Scene Two ends with Edmund pleased at himself and how gullible his father and brother have been.
In Scene Three, Goneril instructs her courtiers and knights to treat Lear poorly. However, this ruse will reveal her true plan which is to outcast her father so that she will have no interference from him in taking command of her portion of the kingdom.
Kent appears in Scene Four (still in Act One), disguised as a servant who wishes to (still) serve the king. Lear is fooled by the disguise and allows Kent to join he and his Fool. It is also revealed that Albany is unaware of his wife's (Goneril's) conspiring plans.
All of the deception in Act One is done out of malice and greed except Kent who uses deception in his endeavor to continue serving his king.