Characters in the series, and likely as not they'll be foils to each other in some way.
- Sheldon doesn't like children, while Leonard likes them.
- Sheldon is socially awkward mostly, while Leonard was initially the same, but grew more socially adept, thus contrasting their way of talking to people.
- Sheldon grows up loved while Leonard grows up unloved.
- Amy is more opening and interested to physical contacts and social conventions than Sheldon is. Sheldon has remained more or less the same, though Amy can actually get him to apologize.
- Sheldon is interested in science fiction, model trains, video games and comic books, while Amy finds them uninteresting though she has been seen participating.
- Amy is able to give gifts, while Sheldon hates doing it.
- Sheldon has a touch phobia, while Amy doesn't, though he has been working on it for her.
- Amy wears glasses while Sheldon doesn't.
- Sheldon never attended middle school or high school, instead starting college at age 11 right after completing the fifth grade in elementary school, while Amy has attended middle school and high school.
- Amy likes playing the harp, old French movies, medieval literature, Chaucer, quilting, the color gray, knitting her own sweaters and garage sales, while Sheldon doesn't share her love for any of these.
- Amy has gotten more anxious to participate in sex, while Sheldon, although he's possessed many thoughts on the matter, still has minor reluctance. The roles were reversed in a Season 10 episode where Sheldon actually did want to have sex but only to procreate and Amy refused as she was not ready to have a child.
Main Characters And Other Characters
- Penny is a community college dropout who isn't thoroughly educated while Priya is an accomplished professional and Cambridge graduate who is highly educated.
- Penny sincerely loves and adores Leonard, she also dates and marries him because he's a nice guy who makes her happy, whereas Priya only dates Leonard as a form of rebellion and is possessive and demanding.
- Penny remains fiercely loyal to Leonard while Priya easily cheats on him
- Unlike Sheldon, Missy is not above physical confrontation, is very charming and amicable, as well as possessing a very cheeky sense of humor.
- As shown in Young Sheldon: Missy is Book Dumb but The Social Expert while Sheldon is a genius who has trouble identifying even the most basic of human emotions.
- Both of them have very different personality traits and parenting strategies. Mary has been a loving and supportive parent while Beverly has been a terrible parent who is pawned by Mary after their first meeting and made to be more motherly towards Leonard.
- Beverly is disliked by the group, while Mary is adored by the group.
- Mary is The Fundamentalist while Beverly is a Hollywood Atheist.
- Alfred and Beverly both are different in terms of personality. Alfred is a nice man who is intellectually interested in religion while Beverly is a horrible woman who considers religion a superstition and even scorns Mary Cooper's Christian faith. Alfred also appears to at least consider the possibility of God existing, while Beverly doesn't.