It’s been a minute since The Big Bang Theory hit our screens in 2007. Over its 12-season run, the series about a bunch of funny nerds introduced us to some really quirky characters. There was Sheldon and his no-filter approach to human interaction, Penny with her sunny disposition, and the awkwardly sensible Leonard. A colorful selection of supporting leads, namely Howard, Raj, Bernadette, and Amy, rounded out the cast.

Each week, fans tuned in to watch this lovable group of friends navigates the complexities of everyday life. Penny outgrew her ditsy qualities, Sheldon got better at picking up on social cues, Howard lost his creep vibe, and Raj was able to talk to women. But Leonard Hofstadter became increasingly irritating over the years, making him the most annoying character in the series.

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Leonard forgives his mother Beverly in the Big Bang Theory

Portrayed by Johnny Galecki, the early seasons focused on Leonard’s lack of experience with women. This explained why he was always jittery around Penny, who was also the girl of his dreams. While that nervous quality made him endearing, his obsessive need to correct others became more annoying as time went on. When Penny reluctantly tells Leonard that she is taking a college history class in “The Extract Obliteration,” he secretly reads and completely rewrites her paper on slavery.

After discovering the extensive corrections, a furious Penny accuses him of assuming her work would be bad. When he patronizingly tells her he didn’t change every word because the dates, her name, and the word slavery are the same, she calls him a jerk, explaining that his behavior is the reason she didn’t want to tell him about her class at all. Leonard’s condescending nature appears throughout the series and stems from his need to be better accepted outside his friend group.

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Leonard and Penny arguing on their wedding night from The Big Bang Theory

He generally thinks he is better-adjusted than his companions and is more willing to try different things. This character trait is evidenced in “The Nerdvana Annihilation,” when he accidentally buys a full-size prop from a television show. While bringing it up to their apartment, the guys inadvertently block the stairs, causing Penny to miss work. After she calls them pathetic for collecting “toys,” Leonard tries to get rid of all his collectibles in an effort to grow up. But he soon backs down from his purge when Penny's friend Mike shows up at her apartment.

However, the most manipulative stunt Leonard ever pulled occurred after he was married to Penny. Having agreed to not have kids with his wife, he suddenly thought it was perfectly all right to serve as a sperm donor to Zack and Marissa. In “The Donation Oscillation,” he even tries to explain his betrayal by telling Penny it’s a chance to leave a part of him behind. But he scraps the idea when Amy reminds him that donating his sperm isn't going to make him a dad. Unfortunately, the show’s writers eventually failed Penny when the couple announced that they were expecting a child in the series finale, 'The Stockholm Syndrome.” Fans were left confused by the move since Penny had always stood by her decision to never have children.

But for all his flaws, Leonard has always served as an anchor to his friend group. If his slightly more sociable, emotionally intelligent approach to life didn’t counteract some of Sheldon’s ridiculousness, the roommates turned best friends would have never met Howard, Raj, Penny, Bernadette, and Amy. As the group’s unofficial mediator, Leonard considers himself Sheldon’s protector, calling his mom when his friend is in distress and ultimately standing beside him as the best man at his wedding. The Big Bang Theory would not have been the same without him.