Schyster is a vehicle manufacturer that appears in GTA 6.
The company made its first appearance in GTA 4, returning in GTA 5 and GTA Online. Schyster was confirmed for GTA 6 in Trailer 1, where a 
One PMP 700 can be seen outside a car meet in 
According to the GTA 5 BAWSAQ website, Schyster is a German company that was bailed out by Americans. The brand's description also claims that Schyster manufactures "unreliable 
The brand appears to be primarily based on the real vehicle manufacturer, Chrysler.
In GTA 6, Schyster appears to have changed its logo from a circular saw blade to Chrysler-esque silver wings.
Given that Schyster is a German-owned company, its name is likely a reference to the word "Scheisse," which translates to "Shit."
This is further evidenced by the brand's BAWSAQ code being "SHT."
