The Arbiter by John Russel Fearn

The thing was of metal—but it walked and thought like a man, and was a grim object of deadly peril and menace!

John Russell Fearn (1908–1960) was a British author and one of the first British writers to appear in American pulp science fiction magazines. Always a highly prolific author, he published not only under his own name, but also as Vargo Statten and other pseudonyms including Thornton Ayre, Polton Cross, Geoffrey Armstrong, John Cotton, Dennis Clive, Ephriam Winiki, Astron Del Martia (and others). He remains best known for his long-running Golden Amazon saga. At times these drew on the pulp traditions of Edgar Rice Burroughs. Fearn also wrote Westerns and crime fiction.