Bart Torgal

Bart Torgal was the heir to Torgal Corp and is the only known child, legitimate or otherwise, of Paul Torgal. He was a beneficiary of advanced learning techniques, having received cerebral implants and learned farming through 'digitraining.' Using this knowledge, he kept the three Degasi survivors alive by growing food.

A few weeks after being marooned, Bart discovered that they were infected with an alien bacterium and attempted to find a cure. Marguerite Maida would bring Bart samples to see how they reacted to the bacteria. However, these were often of little use as Marguerite 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 the reaper leviathan brought back by Marguerite. 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 Marguerite's demise is also shown.

Before the Crash
It's logical to assume that, out of both bias and a desire to see his 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 with taking orders than giving them and prefers studying 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 discovered that the seeds of the bulbo tree, lantern tree, Chinese potato and gel sack were edible, and used his limited technical skills to devise a water purification system. After Marguerite 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 Marguerite. It's also shown that he eventually abandons his base, where he eventually succumbs to Kharaa.

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 Marguerite'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 Marguerite upset Bart, who tries to stay neutral and act as peacekeeper.

Marguerite Maida
Bart and Marguerite are genuinely friendly to one another, with Maida bringing Bart specimens for him to study. Bart is also fascinated with what she will do to ensure their survival, but disagrees with some of Marguerite'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 Marguerite have great mutual respect for each other.

Trivia

 * Bart's original name was Baat, but was changed in later development to Bart.