Leo Spitz, often referred to by his full name Leonardo Ponce de Léon Spitz, is a college student attending Hamilton Hall who becomes Sam Witwicky's roommate during his first year. He is a deeply eccentric and highly excitable individual, consumed by a fervent belief in conspiracy theories, particularly those involving giant alien robots that he insists the government is hiding. To spread his claims, he runs a website called The Real Effing Deal, where he competes with rival conspiracy sites and an online nemesis he calls Robo-Warrior. Leo's personality is marked by a mix of nervous energy, exaggerated confidence, and a genuine desire to uncover the truth, though his methods often lead to awkward or comical situations. His primary motivation is to validate his theories and gain recognition, which drives him to document supposed Transformer activity from the relative safety of his dorm room.

When Sam moves in, Leo immediately tries to impress him with his media empire and his plans to woo a fellow student named Alice, whom he believes is destined to be his wife. This romantic pursuit, combined with his obsessive nature, initially paints him as a somewhat oblivious and self-absorbed character. However, when Alice is revealed to be a Decepticon agent and Leo is captured by the Decepticons alongside Sam, his perspective shifts. Although he panics and attempts to flee, he is eventually rescued by the Autobots and becomes a reluctant but indispensable member of the group. Understanding the global threat, Leo sets aside his rivalries and uses his extensive internet contacts to lead Sam to former Sector Seven agent Seymour Simmons, a figure he had previously clashed with online. This act of magnanimity demonstrates a growing maturity and willingness to cooperate for a greater cause.

Throughout the story, Leo's key relationships include his evolving dynamic with Sam, whom he initially views as a skeptical audience but later treats as a trusted friend and partner in their shared ordeal. His relationship with Simmons is particularly notable; after years of online animosity, Leo extends an olive branch and the two work together closely, with Leo proving his worth by helping to infiltrate the Smithsonian National Air and Space Museum. He also interacts with the Autobots Skids and Mudflap, who consider him a liability at first, but he manages to contribute to the mission despite his evident fear.

Leo's development is marked by a transition from a comic relief figure fixated on internet fame to a capable, if still somewhat accident-prone, ally. During the final battle in Egypt, he accompanies Sam and the others to the Tomb of the Primes, using his skeptical reasoning to question Jetfire's guidance, which ultimately aids Sam in discovering the Matrix of Leadership. He proves his bravery by saving Simmons from being pulled into Devastator's vortex and stands as a true hero by the conflict's end. His notable abilities include a sharp investigative mind, expertise in online research and conspiracy networks, and a surprising resourcefulness when forced into action, even if his physical execution often results in self-inflicted mishaps, such as accidentally tasering himself. Despite his quirks, Leo Spitz embodies the unlikely courage of an ordinary person thrust into an extraordinary situation.