Adrian is a book character and a main character in Das Duell.
Adrian a tomcat with longish red-golden fur and darker brown stripes on that fur. He has glowing yellow eyes, a brown nose, and a color scheme that is altogether very reminiscent of Nhozemphtekh. However, he is not a Felidae cat.
Adrian is young, but lacks the bluster of many other tomcats. Instead, he is levelheaded and intelligent, much like Francis. A keen observer, he comes to logical conclusions if given enough information and his overall brainpower rivals that of Francis himself. He likes to boast at the former's expense.
Adrian shows initial interest in the dead body Francis finds earlier in the story, but only insofar as the point out Francis' mistakes in determining how the cat died. Once that is over and done with, he starts to go off with the females, but Francis insists on his company. Eventually, Adrian does get curious and accompany Francis, which allows the older cat to get closer and suspicious. He begins to think Adrian had a paw in the death of the cat they found, but when accused of this, Adrian denies it. He also gets violent, and the two cats fight it out.
The fight is interrupted by humans and the cats later, where Adrian picks yet more holes in his theories, this time about the Animal Farm business. He accompanies Francis into the corporations more secret holdings, where they store the dead bodies of cats for the purpose of experimentation. Some of the cats are still held captive in the factory, however, and both Adrian and Francis make it their mission to free them.
They part ways at the book's end, Adrian with a teasing, but good-natured comment about their friendship being in jeopardy if Francis came back to compete with him for the females. Also, that he looked better than Francis. The Freed cats since "Somewhere Over the Rainbow" as the story ends.