While there are many examples of strong and inspiring men and women in Genesis, the book is also packed with stories of dysfunctional families, which is evidenced from the very beginning with the first family—Adam, Eve and their two children, Cain and Abel. In no short amount of time—just 16 verses after announcing the birth of Cain and Abel in Genesis 4—Cain has murdered his younger brother and is consequently exiled from the land.
Given that the wife of Cain is only mentioned once in the Old Testament, she would not be counted among the famous women in Genesis. Nevertheless, her identity is still worth investigating. Who did Cain marry? Mary Joan Winn Leith first explores the traditional Jewish and Christian answers that contend that the wife of Cain was another daughter of Adam and Eve. According to this reasoning, Cain would have married his sister—one of Abel’s twin sisters no less, according to the Genesis Rabbah.
Wikipedia goes further and names the sister:
The Targumim, rabbinic sources, and later speculations supplemented background details for the daughters of Adam and Eve. Such exegesis of Genesis 4 introduced Cain's wife as being his sister, a concept that has been accepted for at least 1800 years. This can be seen with Jubilees 4 which narrates that Cain settled down and married his sister Awan, who bore his first son, the first Enoch, approximately 196 years after the creation of Adam. Cain then establishes the first city, naming it after his son, builds a house, and lives there until it collapses on him, killing him in the same year that Adam dies.
From The Book of Jubilees, Chapter 4 at Sacred Texts:
And Cain took ’Âwân his sister to be his wife and she bare him Enoch at the close of the fourth jubilee. And in the first year of the first week of the fifth jubilee, houses were built on the earth, and Cain built a city, and called its name after the name of his son Enoch.
An interesting love triangle theory from Diabolical Confusions:
According to some Hebrew and Islamic scholars, the reason Cain’s heart was not righteous was because of a woman: their sister, Awan. It is believed that Awan was intended for Abel, but Cain fell in love with her. This can be seen in the Book of Jubilees. Adam & Eve had nine (9) children. And this is where the story takes an interesting turn. Genesis, by the way, has no problems with incest, specifically brothers an sisters marrying. That is because there is no other option at this point. So, from this point of view, God has favored Abel in both marriage AND sacrifice.
From Folklore & Mythology Electronic Texts: various versions of the story of Cain & Abel