Toby Loobenfeld

Toby Loobenfeld is a research assistant in the Caltech particle physics lab with a double major in theatre and physics (since his "bourgeois parents" pushed him towards the latter) from MIT, who is cast by Sheldon to play his nonexistent drug addled first cousin "Leopold". However, Toby regards Sheldon's motivation for Leo's substance abuse problem as pop psychology and plays the role as if Leo was abused in the Philippines by a club-footed Navy chaplain when he was fourteen years old. Sheldon becomes disappointed with Toby's portrayal and acting abilities, exclaiming that his parents did the right thing in pushing him towards physics. Later, Toby takes advantage of Penny's comforting attitude toward Leo to snuggle and bond with her, much to the chagrin of Leonard.

Leopold "Leo" Houston
Leopold is a construct Sheldon creates as part of an exquisitely convoluted, "un-unravelable" web to replace a ruse concocted by Leonard that Sheldon deems laughably transparent. After Leonard deceitfully told Penny that he couldn’t come to her performance in a one night showcase production of Rent because Sheldon and him were attending a symposium on molecular positronium given by Dr. Emil Farminfarmian, Sheldon conceives a new lie in which he tells Penny that Leonard was untruthful because he wants to protect Sheldon from the embarrassment of having a drug addled cousin "Leopold" and that they are actually going to participate in Leopold’s drug intervention in Long Beach to convince him to return to rehab.

Believing the success or failure of their deceitful enterprise turns on details, Sheldon creates for Leo a facebook page, an online blog depicting his descent into drug use, and a desperate yet hopeful listing on e-harmony.com. According to the character profile Sheldon wrote for him, Leopold Houston is 26 years old and originally from Denton, Texas, but was a Navy brat, so he was brought up on a variety of military bases around the world - as a result he's often felt like an outsider, never really fitting in, which is probably the reason for his substance abuse problem. As the quintessential middle child, Leo's addiction is meant by Sheldon to be rooted in his unmet need for attention, along with a genetic predisposition to inadequate serotonin production.