The two dogs who played Rex were Reginald von Ravenhorst (aka Santo vom Haus Zieglmayer) and then Rhett Butler. Both were trained by Teresa Ann Miller. Rhett Butler played Rex as a puppy in Baby Rex.
Peter Hajek states that former Pope Benedict XVI was a fan of "Inspector Rex".
No character appears in all of the 119 episodes of the original Austrian version. Gerhard Zemann is credited in every episode, although he is absent from some of them.
Rex changed a lot of his human friends over the 11 seasons, including a famous actor Gedeon Burkhardt.
Detective Richard Moser was named after one of the show's creators, Peter Moser.