The character of August Leffler is played by actress and singer, Shay Astar.
August is Tommy's first serious girlfriend. Intelligent and smart, but also cool and aloof, she seems to be drawn to Tommy because she senses in him a wisdom beyond his years - little suspecting the truth. She does correctly guess quite early on that Dick is not Tommy's real father; telling him that his respect for him is based more on authority than an genuine father-son bond.
While Tommy and August complement each other on many levels their relationship is never smooth. Sex is always an issue for one thing. August is cool and level-headed; a controlling person, almost domineering where relationships are concerned. Tommy, depending on your perspective is either a horny teenager or a dirty old man. She cleverly manipulates Tommy and always has the upper hand.
While Tommy and August both excel academically, are studious and serious it is never quite enough to cement their relationship. August is disdainful towards those she regards as intellectually inferior. She is an ardent feminist who regards those women who don't share her preoccupations as shallow and insignificant. She also has a sharp tongue and a line of put downs that are usually quite devastating.
Adding to the strain on their relationship is that neither one is ever entirely faithful. Tommy has several flings and flirtations while going out with August - including a largely imagined one with their Glee Club teacher. It is August however who eventually terminates the romantic aspect of their relationship when she starts seeing someone else (a student known only as Kevin) behind Tommy's back. They do remain friends of sorts and August continues to be seen in his company as a study partner. On one occasion she even hints at the possibility of them getting back together, asking Tommy if he 'still has feelings' for her. She also comes on to him in the episode where it is revealed that Tommy knows how to cook. By this stage, Tommy appears to have moved on, even if he hasn't found someone else yet.
When August next appears (her penultimate appearance in the show) they find themselves working together on the school newspaper. At this stage Tommy has started dating Alissa and clearly has some confusion about the break-up of their relationship. August feels obliged to remind Tommy that she was the one who broke up with him. Tommy seems to remember it differently. In the end, August makes her point by taking out a full page ad in the school newspaper. It depicts Tommy's face on the body of a jackass - enough said.
According to Wikipedia, August has one final appearance in 3rd Rock - an episode from season four entitled Alien Hunter: "She appeared as a guest at Dick's birthday party, but didn't have any lines. Her appearance in this episode (as well as Alissa's absence) wasn't explained."