K-9, unlike most cyberdogs, is fully sentient and has been modified with vocal organs, allowing him to communicate verbally in several languages. His high intelligence allowed him to develop his own sense of morality, which brought him at odds with Dr. Schreber and his unethical experiments; despite being programmed to work as his assistant, he came to hate the sadistic scientist with a passion. This eventually culminated in him one day biting Schreber, who then punished him by disabling his legs, forcing him to stand still like a statue and watch the doctor's horrible experiments.
After getting his motivator repaired, K-9 was left in NCR by the Chosen One so that he could receive necessary repairs from Dorothy and, not long after his recovery, Dr. Henry (who had been placed in critical condition after being reportedly assaulted by the Chosen One sometime earlier).
Dr. Henry, afraid that too much information about the Enclave would be obtained from K-9, attempted to destroy the cyborg but was stopped by the cyberdog and Dorothy, who suspected what Dr. Henry was planning. The NCR government used the attack as an excuse to confiscate K-9 and the cyberdog in order to learn more information about the Enclave as well as what makes the two of them "tick." At last report (and over Dorothy's objections), K-9 and the cyberdog were disassembled and analyzed. Structural damage during the disassembling is reported to have killed them both.
Fix K-9: He can be found in Dr. Schreber's office at the Navarro facility. He is non-operational when first found and requires some physical repairs.
To obtain K-9, two requirements must be met:
K-9's leg mechanisms must be repaired with a drive mechanism. One is available in the mechanic's shop right on the Enclave base inside a locker. Using this part on K-9 will fix him (this does not require the Repair skill); no other repairs are required.
K-9 will not join if one has low Karma and negative reputations. Moreover, if K-9 is in the party and the player character becomes a Childkiller or their Karma drops below -101, he will leave permanently.
K-9 possesses a sense of humor, and will sometimes make sarcastic and snide remarks during conversations with the Chosen One.
If the player character lies to Skynet about being Dixon while having K-9 waiting outside the Sierra Army Depot, K-9 will turn hostile when Skynet does. This can be fixed by escaping Sierra Army Depot without killing K-9.
His stats are superior to the other cyberdog in Fallout 2, the robodog.
K-9 is one of the few characters that will join a Chosen One with an Intelligence of less than 4.