Laeta Kalogridis and Patrick Lussier were invited to write the script while they worked on another project with David Ellison and Dana Goldberg. They agreed to write a Terminator film when Cameron, a friend of Kalogridis who worked with her in Avatar, gave it his blessing. The starting point of the script was to retain Schwarzenegger as a central character, unlike the Star Trek reboot with Leonard Nimoy as an older Spock in a minor role. They had to write in the actor (now 67 years old), and followed a suggestion by Cameron that the Terminator's living-tissue exterior was vulnerable to aging and their idea of Skynet sending a Terminator after an infant Sarah Connor. Kalogridis and Lussier extended this to the core characters of Kyle, Sarah, and John Connor, despite each being from a different time period. Although the writers reportedly enjoyed Terminator 3: Rise of the Machines, they opted to escape its suggestion that Judgment Day is inevitable because of a causal loop in favor of all Terminator timelines existing simultaneously in a multiverse. To map out the timelines and plot, Kalogridis and Lussier had five whiteboards "covering every wall in the office". They eventually reached a central plot thread in which the Skynet of one universe, defeated in several timelines, sent the T-5000 to the Genisys timeline hoping to defeat the humans by "having the best weapon that humans have": John Connor. The first draft of the screenplay, to attract a director, was delivered in July 2013.