Harry Potter

Harry Potter is a series of seven epic fantasy novels written by British author J.K. Rowling, portraying the adventures of Harry Potter and his companions as they study at Hogwarts School of Witchcraft and Wizardry, and their struggle against the evil Lord Voldemort. The series has since developed into a worldwide booming franchise, containing theme parks and movies. Harry Potter isn't mentioned or referenced as much in the show as other franchises, but Sheldon and Penny have both read the books, and Leonard had already read the first five by "The Spoiler Alert Segmentation".

Episodes
In "The Jiminy Conjecture" (S03E02), Raj says that the fourth Harry Potter movie (Harrry Potter and the Goblet of Fire) was "just fine."

In "The Cornhusker Vortex" (S03E06), Leonard tried to learn football by reading “Football for Dummies" book and watching it on television. Raj is not impressed by the commercials. Howard shows up and Raj is still mad at him. Leonard kept wondering about the stats of the game, such as a sack. Sheldon started describing all Leonard needs to know since his father made him watch football. Howard was astonished that Sheldon knew about football even asking "I mean, Quidditch, sure, but football ...?"

In "The Shiny Trinket Maneuver" (S05E12), while Howard was practicing for his cousin's birthday party and did the trick with the cylinder and brought out a goldfish, Raj says that there's definitely a seat on the Hogwarts Express with Howard's name on it.

In "The Spoiler Alert Segmentation" (S06E15), Leonard was reading Harry Potter and the Half Blood Prince when Sheldon spoils the ending by revealing that Dumbledore dies, igniting an argument between the two. As Leonard storms out, Sheldon also spoils Book 7 by revealing the death of Dobby the Elf to spite Leonard. Later in the episode, Penny accidentally spoils that Harry Potter and Ginny Weasley become a couple to Leonard, much to his chagrin.

In "The Monster Isolation" (S06E17), Raj says to Lucy that "I went to Cambridge, which was wonderful not only because it's a good school but because it totally looks like Hogwarts."

In "The Contractual Obligation Implementation" (S06E18), Sheldon says "I suppose there is a history of professional women using their initials so as not to be pre-judged. Harry Potter's J.K. Rowling."

In "The Table Polarization" (S07E16), Howard shows Raj a magic wand TV remote. The wand is most likely shaped like a wand from Harry Potter. Raj thought it was cool. Raj said that "This is so much better than watching TV like a muggle."

In "The First Pitch Insufficiency" (S08E03), Sheldon reveals that all the guys are members of the Griffith Park Quidditch team, a game based off the sport from the Harry Potter books. "I know, watching your boyfriend run around with a broomstick between his legs isn't something you forget," quipped Penny.