Amy Farrah Fowler is a neurobiologist who was matched with Sheldon when Raj and Howard set him up for a date on a dating website. It turned out that she has characteristics in common with Sheldon and he seemed intrigued enough by her to offer to buy her a beverage (she asked for "tepid water"). Amy revealed to Sheldon that she shares his aversion to soiled hosiery, is completely uninterested in a physical relationship, and that the only reason she was listed on the dating website at all is that she had made a deal with her mother that she would go out on a date at least once every year.
Amy and Sheldon became friends over the next four months, exchanging text messages and emails. They eventually began discussing the possibility of the two of them producing an offspring, assuming that with their superior genetics their child would be a "gift" to humanity. Penny told Sheldon that if they're making plans like that, he should at least get to know her one-on-one, not just by electronic means. Sheldon then asked Amy out on a date and informed Penny that she needed to drive him.
Amy becomes a part of the gang, calling Penny her best friend and joining her and Bernadette for a girls' night (since, as she points out, "I'm a girl") and eating at restaurants with everyone.
Amy is played by Mayim Bialik.