Rexy is a minor antagonist in the FNaF F.R.I.E.N.D.S. series who first appeared in Season 5.
Part 1: Non-Canon
Rexy was the first escapist animatronic of Universal Studios. The tyrant wandered to the pizzeria, and started terrorizing those residing in it. However, when the second escapist, Snappy arrived, it caused problems and Rexy battled the Spinosaurus for a while. Soon, Rexy defeated him, but soon she transformed from an animatronic into a real dinosaur. However, this resurrected Snappy, and the two teamed up until they were carried away by a helicopter to Isla Nublar. Both escaped on an unknown date, and found a portal to another dimension. Neither were seen after, as they had been trapped in after the portal closed on both of them.
Part 2: Canon
Currently, the only things known about the younger part of Rexy's lifespan is that she was born on 1990 on Isla Sorna - an island 207 miles west of Costa Rica, and somehow got to the mainland (Costa Rica).
Part 1: Hatchling and Juvenile years
Barely anything is known about Rexy's early years, and nothing is about her personality.
Part 2: Sub-Adult and Adult years
In her older years, Rexy is rather aggressive to most, excluding Snappy and her offspring, as the twelve all share a family-type relationship. She isn't afraid of anyone, even Arachna. She will fight anything that stands in her way, including things bigger than her.