Oskar Schell is a self-defined inventor, jewelry designer, entomologist, Francophile, vegan, pacifist, percussionist, and collector. Brainy and often socially awkward, he has only a few close friends, most of whom are adults. More than a year after his father's death, Oskar lies awake at night thinking of the different ways his father could have died and then uses his imagination to invent safety mechanisms that would have saved him. Teased at school because he doesn't act or talk as other kids do, Oskar finds solace in searching New York City for the lock that matches the key he found in Dad's closet. His biggest secret is that he didn't pick up the phone when Dad called moments before the north tower of the World Trade Center fell.
Thomas (whom Oskar knows as "the renter") has spent most of his life feeling as though he isn't alive. Raised in Dresden, Germany, he fell in love with Anna at age 15 and planned to spend the rest of his life with her. She, as well as all of Thomas's family, died in the Dresden bombings. Thomas had hoped to become a sculptor, but the physical and mental scars of the bombing prevented him from practicing his art. He moved to the United States to escape his past, only to meet, by chance, Anna's sister— Grandma—in a bakery in New York City. By then, Thomas was no longer able to speak. For basic communication he relies on the YES and NO tattoos on the palms of his hands. For everything else, he uses a seemingly endless supply of notebooks. One day he leaves Grandma and does not return for 40 years. Thomas's life is filled with regrets—not saving Anna, not being a better husband to Grandma, not sticking around to raise his son. By the time he returns to Grandma, he no longer knows any other way to live.
Grandma raised Dad by herself in the apartment across the street from Oskar's eventual home. She is patient, kind, and extremely besotted with her only grandchild, whom she sees and talks to every day. Yet despite their physical proximity, Oskar feels as though he doesn't really know Grandma, who rarely talks about her past. Like Thomas, she has endured more losses than perhaps anyone else in Extremely Loud and Incredibly Close—her sister Anna, her parents, and her son all have died, and Thomas left their marriage with no explanation. Each loss hurts deeply, but Grandma never gives up on life as Thomas does. She is content to be discontent now if it means future generations, such as Dad and Oskar, can thrive. She is particularly set on teaching Oskar not to repeat her own mistakes. Her letters to him emphasize the importance of living life in the wake of tragedy and loving people while there is still the chance. Because she did neither, she believes her life is all the more disappointing for it.
Like Oskar, Mom is still reeling from Dad's death, but her grief shows itself differently from her son's. She attends a support group for people who have lost family members and tries to do her crying while she's alone. Mom isn't looking for love, but she does need a friend, which she finds in Ron, who also has suffered a great loss. Mom's relationship with Oskar has been fraught since Dad died—she's aware that Oskar was closer with Dad and that she won't be able to fill the void he left. She worries continually about Oskar but allows him the freedom to grieve in his own way. Although it appears that she doesn't know or care where Oskar goes on the weekends or what he's doing when he gets there, she works behind the scenes to ensure his safety and preserve his sense of independence. She doesn't always understand or agree with Oskar, but she loves him fiercely.
Dad is Oskar's hero. A lawyer by education but a jeweler by trade, Dad was raised by Grandma. He met his father, Thomas, only once when he went to Dresden and pretended to be a journalist. Like Thomas, Dad didn't enjoy the jewelry business, but he was intent on being "his own father." To Oskar, Dad seemed to know everything about everything. An excellent storyteller and creator of scavenger hunts, he identified as an atheist and refused to believe in aliens. He always read the newspaper with a red pen by his side so he could circle errors. On the morning of September 11, 2001, Dad was at the Windows on the World restaurant at the top of the World Trade Center for a meeting. He didn't make it out alive.