Spencer Shay (Jerry Trainor) is Carly's older brother. When Carly's dad was called overseas, she went to live with Spencer, who turned their loft into both a workspace and gallery for his wacky sculptures. Spencer is off-beat and rarely acts his age, but acts responsibly and seriously when it counts. Though often spontaneous and unreliable, Spencer has been shown as being extremely protective of Carly, especially in episodes such as "iQuit iCarly", when he sees Carly about to fall out of a window and sprints to her rescue, and "iLook Alike", when he would not approve her going to a mixed martial arts fight. In "iWanna Stay with Spencer", when Carly was being sent to live with her grandfather against her and Spencer's wishes, Spencer gives their grandfather Carly's asthma inhaler, despite her not having an asthma attack since she was seven. He tells their grandfather that he had kept all these years in case she needed it and demands he takes it with them, but after seeing how much Spencer really cares about Carly by keeping the inhaler all this time, their grandfather allows her to stay with him. In the alternate reality shown in "iChristmas," it is revealed that if Spencer was born "normal," Carly would have never met Sam and Freddie, Sam would be stuck in a juvenile detention center, Spencer would be engaged to Marissa Benson, andiCarly would not exist.
In addition to making sculptures, he has been shown to be an incredibly talented artist; while trying to teach Carly to draw in "iMust Have Locker 239", he quickly draws a professional-looking rabbit without even looking at the pad, much to Carly's amazement. However, when Spencer tries to get involved in something besides sculpting, it tends to spontaneously set itself on fire as a running gag, despite the object usually not being flammable (such as a cymbal). He is often the focus of the subplot for each episode, in which he usually finds himself in a strange situation. An odd interest of his is dressing up like a woman seen in "iWant My Website Back" and in "iLost My Mind". He also enjoys drinking milk in the shower, as stated in the episode "iGot A Hot Room".
In several episodes, it is stated that Spencer went to law school (because of his father's wishes) for three days before dropping out. Spencer did not tell his father that, claiming that he is busy.
Spencer is constantly being attacked and tortured by a trouble-making boy, who lives in the apartment building, named Chuck Chambers. The conflict started when he was covering for the doorman Lewbert in "iHurt Lewbert". Chuck has been seen in several episodes as a worthy enemy, because of his "sweet" personality, and martial arts skills.
He has also had numerous girlfriends throughout the series, including Veronica from a grocery store (whom he has had a crush on since he first saw her) in "iMake Sam Girlier" and a very high class woman in "iWon't Cancel The Show".
It is revealed that Spencer pulled numerous pranks during his youth in "iGet Pranky". After helping Carly pull a prank, his love for it was reignited, and he soon began to set up constant pranks at the expense of almost everyone, especially Carly. At her wit's end, Carly calls some of his old school friends (all of whom that came were victims from one of his pranks) to talk him out of his refueled habit. When she leaves, however, they resort to beating up Spencer since they still haven't forgiven him for it. Despite this, Spencer gets the message. In "iParty with Victorious" it is shown that Spencer has a book club with only ladies. To Carly, Sam, and Freddie's amazement they think that it is not the most manly thing in the world, Spencer also agrees. In iLost my Mind this book club reappears, exchanging fruit tart recipes.