Leslie Winkle

Leslie Winkle is an experimental physicist.  She's had intimate relationships with both Howard and Leonard, however she is an arch-enemy of Sheldon.  (Perhaps in part due to her misguided belief in Loop Quantum Gravity.)  Leslie is much quicker with a joke than Sheldon so bests him in battles of the wit. 

My favorite Leslie Winkle quote, "Yeah Leslie Winkle!  The answer to the question, 'Who made Sheldon Cooper cry like a little girl?'"

(Leslie Winkle is played by Sara Gilbert)