Serena Joy is a major character in The Handmaid's Tale. She is the Wife of Commander Fred, who is using Offred to try and obtain a child, being unable herself to conceive. In the film adaptation, she is portrayed by Faye Dunaway, and in the television series, she is portrayed by Yvonne Strahovski.
In the novel Edit
Offred states that Serena Joy's real name is Pam, and that Serena Joy is a stage name. Before the creation of Gilead, Serena was a televangelist and talented singer, who advocated for women to return to 'traditional' family values and roles and supported Gilead's creation. At some point, she married a man named Fred, who became a high-ranking Commander in Gilead. However, after Gilead's triumph, Serena was left bitter and miserable. She was stuck at home all day and had to rely on Handmaids to conceive a child.
Serena Joy is apparently aware that the Commander breaks rules in regards to keeping contraband items, but turns a blind eye out of love for him. She herself smokes cigarettes, a banned item. What she does not tolerate though, is her husband becoming too familiar with their Handmaids. When Serena found out that Offred's predecessor had been visiting her husband behind her back, she was furious. It is implied that the Handmaid committed suicide partly out of fear as to what Serena would do. Serena makes it plain that she doesn't like Offred, but views her as her only chance to gain a child. She secretly strikes a deal with Offred, arranging for her to meet with Nick in private - whom he trusts - so as to conceive, stating that many Wives do this. She offers Offred cigarettes and information on her daughter - whom Offred has not seen for years - in exchange.
When Serena learns that Offred has been conducting an emotional affair with the Commander, after finding lipstick stains on her blue shawl (which Offred had worn as a disguise when she visited Jezebel's with the Commander), Serena Joy angrily confronts her, asking how she could betray her like this after she tried to help her. When Offred is arrested by the Eyes, it becomes apparent that Serena Joy did not turn her in in revenge, as she looks horrified and calls Offred a "bitch", apparently believing Offred had reported Fred to the Eyes in either revenge or an attempt to save herself.
The epilogue discusses Serena Joy's real identity; the most likely candidate for her husband is Commander Fred Waterford, however, his wife's name was Thelma, not Pam; the other most likely candidate did not have a wife named Pam either. This would suggest that Offred misremembered Serena's real name, that she is a completely different person or even that Offred used a false name for some reason; using Serena's real name could've identified Offred, endangering her loved ones, or it's possible that, despite Serena's generally horrible treatment of her, Offred was attempting to protect Serena herself, as she would likely have gotten into a great deal of trouble for helping Offred commit adultery with Nick.
In the Hulu series Edit
Serena Joy is portrayed by Yvonne Strahovski. In this adaptation, Serena Joy seems to be portrayed as being younger (in her thirties) than she is the novel, where she is implied to be middle aged, though she is still apparently infertile.
In Episode 6, it is revealed that she and her husband, Commander Fred, had a role in orchestrating the alleged "terrorist" attacks that killed all those in Congress, the White House, and the Supreme Court; and helped established the Republic of Gillead's regime. Though Fred was reluctant upon receiving news that the attacks were given the confirmation to proceed, Serena was confident that the staged attacks themselves would help quickly propel the envisioned society that was conducive to her own theocratic beliefs. The episode also reveals that she thought of fertility as a natural resource, and presented it as such to Mrs. Castillo, the Mexican Ambassador leading her country's trade delegation, who was intrigued by the idea of Handmaids. Ambassador Castillo later revealed to Offred that Mexico also suffers from infertility and that her country "is dying" as a result of several years without the successful birth of a child.