Bart Torgal

Bart Torgal was the heir to Torgal Corp and is the only known legitimate child of Paul Torgal, though the PDA implies he has illegitimate half-siblings. He was a beneficiary of an advanced learning program through which he learned farming techniques amongst other things. Bart was also the recipient of a cerebral implant, presumably enhancing cognitive abilities. Using his knowledge, he kept the three Degasi survivors alive by growing food.

A few weeks after being marooned (when they had reached the Deep Grand Reef), Bart discovered that they were infected with an alien bacterium and attempted to find a cure. Marguerit Maida would bring Bart samples to see how they reacted to the bacteria. However, these were often of little use as Marguerit tended to severely injure or use Transfuser serums on the creatures, making them unsuitable for testing.

Bart's last known location was the western observatory on the Floating Island, to which he fled after the destruction of the Deep Grand Reef base by a Reaper Leviathan that followed the one brought back by Marguerit. He made a final log, detailing the effects of the Kharaa on him and noting that he would soon join his friend and father in death.

Bart provides the voiceover for the official cinematic trailer of Subnautica, a slightly edited version of his third and final log "Return From the Deep." A brief snapshot of his life after Paul and Marguerit's supposed demise is also shown.

Before the Crash
It's logical to assume that, out of both bias and a desire to see his only legitimate son succeed as heir to the family empire, Paul would have installed Bart as his second in the shipboard hierarchy. This position would very likely have been an uncomfortable one for Bart, as he seems to have little experience and no interest in a command situation. Judging from the logs found throughout the game, Bart is much more comfortable taking orders than giving them, preferring instead to study the local biodiversity.

After the Crash
After crashing on 4546B, Bart immediately sets to finding a way to ensure they don't starve by determining which plants were safe to eat and which ones were not. He eventually grew Chinese Potato Plants and Marblemelon Plants, and used his limited technical skills to devise a purification system that would desalinate and clean the seawater to create potable water for them to drink.

After Marguerit and Paul died, it's shown in the cinematic trailer that Bart survived for some time and was able to build himself a base in what appears to be the Safe Shallows or the Crash Zone, a Seamoth and gather several pieces of lab equipment. It's possible that he discovered a purple tablet during this time, as the only other one found by the Degasi crew was an Orange Tablet uncovered by Marguerit. It's also shown that he eventually abandons his base and flees to the Floating Island, where he makes his final log.

Personality
Bart has an interest in plants, as noted by his father, and has received cerebal implants. Bart had a great interest in the wildlife of Planet 4546B, often disapproving of Marguerit's methods, asking in one log what the point of surviving the planet was if they had to kill everything that made it wonderful. After the destruction of the Deep Grand Reef Seabase, he seems to be accepting of his fate, and unfazed by the death of his father and friend.

Paul Torgal
Despite being his father, Bart doesn't seem to be particularly close to Paul. It can be noted that Paul appears to be overprotective over his son, which may be due to the fact that they are on an alien world and Paul is fearing for his safety. It can also be noted that the frequent fights between Paul and Marguerit upset Bart, who tries to stay neutral and act as peacekeeper.

Marguerit Maida
Bart and Marguerit are genuinely friendly to one another, with Maida bringing Bart specimens for him to study. Bart is also fascinated by her willingness to do everything in her power to ensure their survival, but disagrees with some of Marguerit's methods of getting creatures for him to study and can get upset when she severely injures them or injects them with Transfuser serums. Despite this, he and Marguerit have great mutual respect for each other.

Trivia

 * Bart's original name was Baat, but was changed in later development to Bart.
 * Bart and his father shared the surname of Torgaljin before it was shortened to Torgal.
 * Bart describes seeing visions upon nearing death. It is possible that they were in fact from the Sea Emperor Leviathan attempting to communicate with Bart.