Alonzo Alfred Aloysius K'Tah, nicknamed "JB", is a time agent from the future as well as a main character in The Missing series. He got the nickname JB (short for "Janitor Boy") after posing as a janitor for the FBI in Found.
JB has brown hair, green eyes, and is described as cute by Katherine in Found. JB feels a great sense of responsibility of his duty, and easily gets irritated and stressed out whenever anything in time gets altered. Despite this, JB eventually begins aiming to save people as well as time. JB is kind, intelligent, brave, and has been seen to joke around with Jonah, Katherine, and Hadley, despite his seriousness for his job. Jonah and Katherine did not trust JB until about the third book.
JB is first seen by Jonah and Katherine at James Reardon's office. Jonah and Katherine assume he is actually a janitor and nickname him JB. As a time agent, he opposes Interchronological Rescue, specifically Gary and Hodge and their plot to sell the missing children in the future. He instead wants to send all the children back in time to their rightful positions in history to prevent time from collapsing.
WARNING: HUGE SPOILERS Edit
In Caught, it is revealed that JB's real identity is actually Tete Einstein, son of Albert and Mileva Einstein. As a result, this also makes him the brother of Emily, who was originally Lieserl Einstein. As Tete, JB had mental illness, schizophrenia to be exact. When he was a teenager, his mother unaged him into a baby and sent him to the future where he grew up and became a time agent. His mother also brought in another mentally ill youth from the past to replace Tete in time, allowing it to flow properly.