Played by: Rene Auberjonois
Position/occupation: Security officer in Bajoran militia
Rank/title: Chief Security Officer, Deep Space Nine
Birthplace or childhood home: Founders' homeworld; Bajor (research lab)
Family: None, unless you count the entire Great Link. Dr. Mora was an early father figure to him.
Love interests: Kira Nerys, Arissa
Spouse: Lwaxana Troi (for a few months in 2372; the marriage was annulled)
Friends elsewhere: Unnamed Bajoran peace officer (seen in "The Circle"); a couple of friends in Starfleet Intelligence
Hobbies/likes/interests: Odo was known to go kayaking with O'Brien, and to read detective novels. Quark also once caught him reading a romance. A speech of Odo's in "A Man Alone" might be interpreted to mean that he liked Karo-Net and Earth jazz.
Dislikes: Odo never learned to gamble, and apparently did not care for Klingon opera.
Shortly after being "formed", Odo was sent away from the Great Link as one of 100 infant explorers; until the beginning of the third season of the show, he did not know what he was or where he had come from. Having at some point passed through the wormhole to the Alpha Quadrant, he was discovered in the Denorios Belt by Dr. Mora Pol, and brought to the Bajoran Center for Science. The name he ultimately went by, Odo, was derived from the label on the beaker he rested in: "odo'ital", Cardassian for "unknown sample", or, literally, "nothing". Odo was studied by Mora, who saw to his education, and he tried to fit in by using his shapeshifting abilities to entertain others. Eventually Odo learned to take humanoid form.
After being the main attraction at a reception for the Cardassian High Command, Odo had an argument with Dr. Mora, and left the research center. He apparently spent some time in the mines, where he was often asked to settle disputes among the Bajorans, as he was considered a neutral observer. Then Odo was forced by Gul Dukat to investigate the murder of Vaatrik; his first criminal case. Kira was the prime suspect, but he let her go when she convinced him she was elsewhere committing sabotage at the time. Odo became chief of security on Terok Nor, and once arrested three Bajorans -- Timor, Ishan, and Jillur -- for an assassination attempt on Gul Dukat. After they were executed, Odo discovered evidence that they had been innocent. He deeply regretted the incident, which probably motivated his dedication to justice above the rule of law.
Odo remained as security chief when Starfleet took the station over ("Emissary"). In "A Man Alone", when Ibudan, a black marketeer Odo once arrested, was found murdered in a locked holosuite, Odo was accused of the crime, and ostracized by station residents, until it was found to have been a frameup. Odo was later tantalized by the claims of a prisoner, Croden, that he knew where other "Changelings" lived. He never totally believed this, but ended up letting Croden go ("Vortex"). Odo was the unwilling recipient of Lwaxana Troi's affection in "The Forsaken"; and in "Dramatis Personae" was the only officer not affected by the Saltah'nah matrix, which he managed to find a way to neutralize.
In "Necessary Evil", Odo recalled his first murder case, and realized that Kira had killed Vaatrik after all, a fact which strained their friendship. Soon after that, he was reunited with Mora, who had news of the discovery of DNA similar to Odo's in the Gamma Quadrant. During an expedition there, Odo was affected by a volcanic gas which caused him to unknowingly go on shapeshifting rampages; but he was eventually cured, and reconciled with Mora ("The Alternate"). In "Shadowplay", Odo went to the Gamma Quadrant with Dax, and investigated mysterious disappearances in a village that turned out to be made up of holograms; one of them was a little girl named Taya whom he befriended.
On the mission to locate the Founders in "The Search, Parts I and II", Odo finally found his homeworld and people. However, when he learned that his people were the Founders of the Dominion, he rejected them and returned to DS9. Odo hoped to correct some of the wrongs committed by his people when he tried to teach a young Jem'Hadar boy to curb his violent tendencies, but he failed and finally returned him to the Jem'Hadar ("The Abandoned").
At around this time, Odo came to realize that he had fallen in love with Kira, who was unaware of his feelings. He acknowledged it to himself in "Heart of Stone", when Kira was trapped in a crystal; thinking that she was about to die, he confessed his feelings, but then learned to his chagrin that she was actually the Female Changeling, impersonating Kira to try to sever his allegiance to the solids. Odo continued to keep his secret until "Children of Time" in the fifth season.
In "Improbable Cause"/"The Die is Cast", Odo's investigation of an explosion in Garak's shop led to the discovery of a massing joint fleet of the Obsidian Order and the Tal'Shiar. Although he was tortured by Garak while a prisoner on a Romulan ship, Odo saved Garak's life during the battle and escaped with him. Some time after this, while Odo was "hosting" Curzon Dax in Jadzia Dax's zhian'tara, Curzon decided to stay (apparently with Odo's consent), but was eventually persuaded to return to the symbiont. Then, in "The Adversary", Odo killed another Changeling to save his crewmates on the Defiant, thus breaking the Changelings' law against harming others of their species.
While guarding Shakaar during the First Minister's visit to the station, Odo watched in secret agony as Kira and Shakaar entered into a closer relationship. Surprisingly, it was his enemy Quark who realized what Odo was going through and gave him counsel ("Crossfire"). Odo withdrew from Kira, and later, in "The Muse", aided a pregnant Lwaxana by marrying her as a legal technicality to help her keep custody of her unborn half-Tavnian son. (The marriage was assumed to have been annulled in a few months.) Then, in "Broken Link", the Founders gave Odo a deadly illness to force him back to the Great Link to be judged for having killed another Changeling. They punished him by taking away his shapeshifting abilities, locking him into solid form as a human, though still with his "unfinished" face.
In "Apocalypse Rising", Odo was disguised as a Klingon for the mission to Ty'GoKor, along with Sisko, O'Brien, and Worf; and he was the one who realized that Martok, not Gowron, was the Changeling. A bit later that year, after passing through a space anomaly, Odo telepathically "linked" with Sisko, Dax, and Garak, causing all four of them to relive a shameful incident in Odo's past -- the incident where he had unjustly arrested the three Bajorans ("Things Past"). Then, in "The Ascent", Odo was stranded with Quark on a hostile planet, and the two of them had to climb a mountain, carrying a subspace transmitter, and fighting all the way.
When Odo came into possession of an injured baby Changeling, he tried to teach it to shapeshift, with unwanted help from Dr. Mora. They met with some success before it eventually died, but in its last moments it integrated itself into Odo's body, and he was able to shapeshift once more ("The Begotten").
In "A Simple Investigation", Odo fell in love with a woman named Arissa who came under his protection as she was trying to leave the Orion Syndicate, and who became the first humanoid woman he was ever intimate with. He eventually learned that she was a deep-cover Idanian agent. When Arissa regained her true memories, she realized she was married, and left Odo to return to her life. It was not long after this that Odo was on a mission of the Defiant in the Gamma Quadrant where the crew encountered their own descendants. Odo was unable to take humanoid form through most of the adventure, but learned through a link with an older version of himself that Kira now knew of his feelings for her. Their new understanding, however, was shadowed by the fact that the older Odo had wiped out the existence of 8000 colonists to save Kira's life ("Children of Time").
Odo remained on the station when the Dominion and Cardassia took over in "Call to Arms"; and in "A Time to Stand", he joined Dukat and Weyoun on the station's ruling council, in exchange for re-establishing Bajoran security. In "Behind the Lines", when the Female Changeling visited, Odo linked with her, and under her influence ceased to care about the solids or the war. Thus, he failed to aid in the plan to prevent the minefield from being destroyed, leading to Rom's capture. Kira was furious with him for this, which only vaguely disturbed Odo, until finally, in "Favor the Bold"/"Sacrifice of Angels", he learned that Kira had been arrested and would be executed. He then broke free of the Female Changeling's influence and led a Bajoran security force which prevented Kira's and Rom's recapture after their escape.
Odo's reconciliation with Kira was (frustratingly) handled offscreen in "You Are Cordially Invited". Finally, in "His Way", Odo began consulting Vic Fontaine for advice on how to win Kira's heart. At a "practice" date with what he thought was a hologram of Kira, Odo learned that she was the real thing. He left the holosuite in mortification; but the next day, she confronted him, and their argument led to an impulsive and very public kiss, which was the beginning of their romantic relationship.
After paying back his debt to Quark for his role in aiding his love life, by deliberately ignoring a smuggling deal (in "The Sound of Her Voice"), Odo had his first argument with Kira as a couple in "Tears of the Prophets".
In "Treachery, Faith and the Great River", Odo went to meet a Cardassian informant, but instead encountered Weyoun 6, who said he wanted to defect to the Federation. Odo then found himself fleeing the Jem'Hadar. Among other things, he learned from Weyoun 6 that the Founders were dying of a disease which had spread through the entire Great Link; Weyoun believed that Odo, as the last of his kind, could reform the Dominion. When escape seemed impossible, Weyoun 6 finally suicided to save Odo, who blessed him as he died.
Later that year, in "Chimera", Odo encountered Laas, one of the other 99 Changeling explorers, and was torn between his love for Kira and his desire to join Laas in a quest for their siblings, and live as Changelings "were meant to". When Kira freed Laas from a holding cell and directed Odo to a rendezvous point, Odo finally realized that she loved him enough to let him go, and he chose to stay with her.
Just before leaving with Kira on a mission to aid Damar, Odo provided Bashir with a sample of "goo". On the way to their destination, Odo learned from Bashir via subspace that he had contracted the Founders' disease. Later, he noticed the first symptoms ("When It Rains..."). Due to frequent shapeshifting over the next weeks, in "Tacking Into the Wind", Odo's condition deteriorated rapidly, though he tried to hide this fact from Kira. He was unaware that she knew the truth. After they captured a Jem'Hadar ship, Odo finally collapsed. (Note: in this episode, Odo imitated the Female Changeling; the only time we ever saw him impersonate a specific sentient being.) Kira brought him back to DS9, and left again at his insistence; eventually, Odo was finally cured by Bashir ("Extreme Measures"). He learned in "The Dogs of War" that he had been deliberately given the disease by Section 31, who used him to introduce it into the Great Link.
In "What You Leave Behind", Odo was on the Defiant during the final assault against the Dominion. After Kira and Garak had captured Dominion headquarters on Cardassia Prime, Odo beamed down and linked with the Female Changeling, curing her and in return gaining her agreement to cease hostilities and stand trial. This brought the final end of the war. Odo chose to rejoin the Great Link in her place, so that he could heal his people, and also in the hopes that he could teach them not to fear "solids" any longer. Kira took him to his homeworld, and they parted on the shores of the Great Link.
Other facts: Odo was an adept reader of body language, and never carried a weapon even as part of his job. For the first two seasons, he had no quarters, resting instead in a bucket in the back of his office. Spiritually, he was an agnostic. His blood type, while he was human, was O-negative.