Adam Sackler is a young 20-something artist in New York City, and Hannah's main love interest. He is portrayed by Adam Driver.
From the Official Site:
"Adam is the guy Hannah sleeps with sometimes -- when he decides to answer her texts. He's an actor-writer-woodworker (triple threat!) with a small subsidy from his grandmother and a love of dirty talk and even dirtier sex. There might be more to him than meets the eye, but it's going to take Hannah some time to figure it out. Meanwhile, she will continue to show up on his doorstep dressed as a sex witch."
At the start of the third season, Adam and Hannah are living together as a couple. In the later episodes, he is cast in a Broadway production of George Bernard Shaw's Major Barbara and his schedule starts taking a toll on his relationship with Hannah.
At the start of the season, Adam has become a full-time actor, having done an anti-depressant commericial.