J. F. Sebastian/John R. Isidore (c. 1994 – November 2019) was a genetic designer employed at the Tyrell Corporation.
"...I make friends. They're toys. My friends are toys. I make them. It's a hobby. I'm a genetic designer." - J.F. Sebastian to Pris
J.F. Sebastian, although 25 years old, looks significantly older. He suffers from a medical condition called Methuselah Syndrome, meaning his glands "grow old too fast" thus leading to accelerated aging and an early death. His condition caused him to fail passing the medical examination to leave Earth for the Off-world Colonies, and so J.F. lives by himself in the Bradbury Building, given to him by Eldon Tyrell.
Sebastian is a gifted genetic designer, evident by his production of his "friends", equal part toy and organic. Although countless creations are strewn about his apartment, the two most significant are the Kaiser and the Napoleonic bear. Besides this, Sebastian worked with Tyrell to develop Nexus-6 replicants, specifically their nervous system.
Sebastian also had a fondness for chess, playing solely with Tyrell and only managing to beat him once.
Events of 2019
Encounter with Ray McCoy
Blade Runner Ray McCoy, after having been rendered unconscious whilst pursuing leads at the Bradbury Building by Sadik and Clovis, can return to the Bradbury Building and speak with J.F. Sebastian about the deaths of fellow geneticists Marcus Eisenduller, Moraji, and the whereabouts of Luther and Lance. If McCoy asks too many questions or brings up anything regarding replicant Nexus-6 information, Sebastian will realize McCoy is a Blade Runner and ask him to leave, refusing to answer further questions. One of the four DNA data chips on furthering replicant lifespans can be found on Sebastian's computer, which must be turned on and resumed in order to collect.
Meeting the Replicants
In 2019, six Nexus-6 replicants escaped the Off-world Colonies and came to Earth to find a way to prolong their 4 year lifespans. Led by Roy Batty, these replicants began to infiltrate the Tyrell Corporation and interrogate scientists in order to glean information about replicant life span alteration.
Hannibal Chew, an eyeball manufacturer on DNA Row, reveals to Batty and Leon that J. F. Sebastian can take them to meet Tyrell in person. This prompts replicant Pris to stage a run-in with Sebastian, playing a lost, hungry, homeless person. Sebastian invites Pris into his home, allowing her to contact Batty and alerting him of Sebastian's location. After the deaths of Zhora and Leon, Batty meets up with Pris at Sebastian's apartment in the Bradbury Building.
Sebastian and Roy
"There's some of me in you." - J.F. Sebastian to Roy Batty
Sebastian is excited to discover that his new friends are Nexus-6 generation replicants, and his condition gave him something in common with them (namely accelerated aging). Batty brings this up, manipulates and then morally squeezes Sebastian into helping Batty get to Tyrell. The deciding factor in Roy's manipulation of Sebastian is a chess game in progress against Tyrell. The two opponents have chess boards in their homes; the pieces are arranged identically on both boards. Roy is seen studying Sebastian's board and is able to discern two moves that will win the game for Sebastian.
Confronting Tyrell and Death
After arriving at the Tyrell Corporation, Sebastian nervously relays the winning movements to Tyrell, who grants him access to his living quarters. Upon meeting his "maker", Roy demands an extension of his life and a brief discussion follows. Infuriated at Tyrell's inability (or unwillingness) to grant him longer life, Roy crushes Tyrell's skull and then murders Sebastian before fleeing.
Deckard receives news of Sebastian's death from Bryant, and is ordered to investigate the Bradbury Building for any sign of the remaining two replicants.