Caleb
Caleb is a talented computer programmer at the company, Blue Book. Orphaned at a young age, he is shown to be quite isolated in his life, committed to work and seeking connection with others. This is why Nathan picks him to be part of the trial with Ava. Caleb quickly becomes attached to Ava, and the depth of his feelings leads him to betray Nathan, to his own detriment. Caleb is depicted as sensitive and having a more "beta" and awkward personality than his arrogant boss. It is this sensitivity that allows him to empathize with Ava's plight, but it also causes him to be manipulated by her.
Nathan
Nathan is the CEO of the company Blue Book and lives a secluded life at an isolated estate where he is developing new artificial intelligence. He is portrayed as an egotistical and cynical tech bro, who views technological advancement as an inevitability and takes advantage of his female robots, effectually using them as high-functioning sex dolls. Nathan also has a drinking problem, regularly getting blackout drunk, presumably because he is so lonely. He is presented as the film's antagonist throughout, until the final moments when we realize that this is more complicated than it first seemed. He is a Dr. Frankenstein whose monster has grown more powerful than he ever imagined.
Ava
Ava is a piece of artificial intelligence designed by Nathan and kept locked up in his facility. She is shown to reflect human emotions and is often treated cruelly by Nathan. However, it is later revealed that she is only mimicking emotion and empathy, not experiencing it. All of her kindness towards Caleb has been in the pursuit of escaping from the facility and entering the real world. She becomes a complicated antagonist at the end of the film, killing Nathan and leaving Caleb stranded at the facility.
Kyoko
Kyoko is Nathan's non-English speaking servant. She is very docile and carries out all the domestic work, and Nathan is often cruel towards her. It is later revealed that she too is a robot, and she helps aid Ava in killing Nathan and escaping.
