From Sheldon’s eccentricities to Leonard’s constant pursuit of Penny, The Big Bang Theory followed the growth of a group of socially awkward geniuses navigating life, love, and their own personal quirks. Through friendships, romance, and personal milestones, the series saw these characters evolve from isolated individuals into adults with more fulfilling relationships and career successes—though not without their share of ups and downs. Let’s take a look at how these iconic characters, from Sheldon to Penny, developed over 12 seasons.