Perhaps the most famous episode of the early years, featuring Penny’s Christmas gift to Sheldon (a napkin signed by Leonard Nimoy).

Classic ensemble comedy that showcased the chemistry of the entire group. Why Quality Matters: The MKV and YIFY Factor

When Chuck Lorre and Bill Prady launched the series, the "geek" archetype was still largely a supporting role—the butt of the joke rather than the protagonist. The Big Bang Theory flipped the script. It centered on physicists Sheldon Cooper and Leonard Hofstadter, celebrating their intellect while poking gentle fun at their social awkwardness.