Saru was a Kelpien from Kaminar who became the first Kelpien Starfleet Officer after messaging with Lieutenant Philippa Georgiou. He would later become acting Captain of the USS Discovery before assuming full captaincy after the Discovery moved 930 years into the future.
Kaminar is a planet with two civilizations. The Ba'ul and the Kelpiens. The Ba'ul are a spacefaring race that has subjugated and culled the Kelpiens to keep them from again becoming the dominant race on the planet. The Kelpiens, when Saru joined Starfleet, were not warp capable, and thus the Prime Directive kept full contact from occurring. Kelpien society is agrarian and culled regularly by the Ba'ul as they take any Kelpiens experiencing a condition called the va'hari. Saru did not accept and questioned the place of Kelpiens in the universe.
A Ba'ul ship crashed near Saru's house. Instead of disposing of the wreckage like he was told to by his Father, Saru built a communications device with it. He reached out into the stars and found Lieutenant Philippa Georgiou of the USS Archimedes. She was granted special permission to take Saru off Kaminar with the cost being he could never return to the planet as long as the Kelpiens were a pre-warp society. He left taking with him a knife that had belonged to his sister, and a handful of Kaminar plant seeds.
He was granted refugee status by the Federation at Starbase 7. It was here that Saru first saw the magnitude of the diversity of universal life in all its forms. He was moved by what he heard of the other races of the vast Federation and its utopian lifestyle and dedicated his life to Starfleet and helping others.
As he was the first Kelpien to join Starfleet, he felt that he had to make the very best first impression by pushing himself hard, ultimately too hard as it impacted his health in his attempts to succeed. He learned 94 Federation languages and became a specialist in first contact.
Saru was reunited with the now Captain Georgiou aboard the USS Shenzhou serving as her science officer. He had attained the rank of lieutenant and worked as a bridge officer.
Saru was promoted to lieutenant commander before the Battle of the Binary Stars in 2256, a battle that started the Klingon War. Before the battle, it was Saru who predicted that death was coming and also who detected biometric changes in Lieutenant Commander Michael Burnham when she attempted mutiny to fire on a mysterious Klingon ship before it fired on them.
After the battle and the death of Captain Georgiou, Saru was again promoted and became Number One to Captain Lorca aboard the USS Discovery. When the prison transport containing the fallen mutineer Michael Burnham was rescued by the Discovery, Saru made his feelings about how Burnham had failed Georgiou clear by telling her, "I intend to do a better job protecting my captain than you did yours."
Saru's relationship with Burnham remained wary for quite some time. He attacked her and Lieutenant AshTyler when on a mission to the planet Pahvo to keep its inhabitants out of the war. with the Klingons. Their psychic energy and abilities disabled the constant fear that Saru and all Kelpiens live with from birth to their culling by the Ba'ul. He enjoyed this lack of fear so much that he refused to leave until the Pahvo inhabitants released their psychic hold on him.
After using the Discovery's spore drive to help achieve victory over the Klingons, the crew of Discovery found themselves in unknown territory... The Mirror Universe.. a harsh alternate universe where everything is opposite what it is in our own universe.. A universe that is even harsher for Kelpiens. The Mirror Saru is a slave aboard the ISS Shenzhou that saved Burnham when the unknown hidden Klingon personality in Tyler activated and tried to kill her. When reporting to the primary verse Saru, Burnham lies about there being other Kelpiens to protect him from the unsavory truth. After learning the truth about Captain Lorca's duplicity that he was in fact a mirror verse person instead of a Prime Universe person, Saru takes command of Discovery and orders the destruction of the Charon, Terran Emperor Georgiou's base ship, and uses the shockwave from its destruction to travel back to their own universe.
The pilot of the spore drive, Lieutenant Paul Stamets did not get the timing of the jump back to the Prime Universe right and accidentally jumped the Discovery 9 months farther in the future in the war with the Klingons than intended. The Federation was on the brink of total defeat. However, thanks to a daring plan, the war was stopped, and Saru was awarded the Starfleet Medal of Honor for his actions.
Saru shared command of the Discovery with Captain Christopher Pike while they investigated strange "red bursts" randomly seen around the galaxy. Saru believed the red bursts could have been either temporal anomalies or possible black holes.
When the USS Discovery encountered a probe that was actually a sentient being, it triggered what Saru believed to be a terminal disease called the vahar'ai. His threat ganglia, which reside behind all Kelpians ears, grew distended and swollen and with no known cure, the "disease" would lead to madness and death. He asked Burnham to cut them off to end his agony and euthanize him as the Ba'ul do in the culling, but before she could, the ganglia shriveled up and fall off. Saru didn't die and instead, lost the fear that had affected him for his entire life. He reported that he felt his "own power" now.
He also realized that the "Great Balance" of the Ba'ul was a lie. His body continued to change and the threat ganglia were now replaced with spikes in slots like teeth.
When a new signal from the Red Angel appeared over his homeworld, the USS Discovery raced there. The crew reviewed the Sphere data on the Kelpiens and found that over 2,000 years ago, the Kelpiens were at the top of the food chain and the Ba'ul were almost driven to extinction by the Kelpians. Burnham and Saru transported to the surface to meet Saru's sister, Siranna. They also saw the notorious Ba'ul Pylons, structures that transported Kelpiens to be culled and also equipped with weapons capable of destroying an entire village if the Kelpians resisted. Every Kelpien Village had one. It activated and the Away Team was beamed back to the Discovery, leaving Saru distraught about his family. The Ba'ul hailed Discovery and threatened them about breaking the Prime Directive, in that Saru is their property. Captain Pike defended him, saying he was a political asylum seeker and a Starfleet officer, protected by the Federation. The Ba'ul questioned why Pike would risk his own people for one Kelpien, to which Pike replied that Saru was one of them. He would protect him and do what he deemed necessary. The Ba'ul replied that they would do the same and Discovery's scanners showed that the Ba'ul had activated the pylon in Saru's village.
Saru caused a disturbance which had Pike order him off of the bridge. He went to the transporter room, where Burnham confronted him. She didn't stop him and he transported over to the Ba’ul ship after using a delayed transport. The Ba'ul restrained Saru and his sister Siranna aboard their ship. They were to be studied before being destroyed. Saru found new strength in the rage he felt and destroyed the probes that were to study them.
Using the Sphere information, he broadcasted a similar signal that the sphere had used to trigger the vahar'ai in all of the Kelpians on their planet. He was 62% successful. However, the Ba'ul were ready to commit genocide to prevent losing their control over the Kelpians. The Discovery couldn’t target all of the pylons in time, but saving the day, the Red Angel appeared and sent out an electromagnetic pulse which disableed the pylons. Siranna returned to heal the planet without fear.
Captain Pike returned to the USS Enterprise, and both ships battled Section 31, Starfleet's intelligence organization, and the threat behind it called Control which was an AI bent on getting the vast data and knowledge of the Sphere that now lived on within Discovery. The Red Angel's goal was to keep Control from winning and wiping out all sentient life in the universe. Saru would attain command of the Discovery and with the approval of his crew, took the ship and the Sphere data 930 years into the future. He became Captain of the Discovery, and Michael Burnham, his once rival and mutineer, became his Number One.
In this new future, Saru had found it challenging to fill the shoes of the Captains he has followed and respected in his career. The connection that those captains had with their crew seemed "effortless" to them, but not to him. He attempted a meal with his bridge staff that resulted in the messy emotional revelations of strife affecting the crew as they dealt with the loss of their families and everything they had once known. It healed more than it broke, and the crew came together to watch the comedy of Buster Keaton on a movie night for the crew to relax and bond.
From fear to curiosity to real strength, Saru's journey as a Starfleet officer continues..