He worked as slush-pile reader for New York-based magazines, and at night he wrote his own short stories — things that did not often advance past the slush pile. In fact, he received 204 rejection slips before his first short story was ever accepted. But soon after that, the first novel he wrote was accepted by Random House. It was called The Mercenaries (1960), it was huge best-seller, and it was nominated for the prestigious Edgar Allan Poe Award from the Mystery Writers of America.
He wrote fast, sometimes publishing four books a year. Publishers had reservations about releasing multiple titles in one year by a single author. And for this reason — especially early in his career, when he was furiously prolific — he used pen names. Mystery novelist Donald Westlake was also mystery novelist Richard Stark, and he was Curt Clark, and Timothy J. Culver, and Tucker Coe. And he was Samuel Holt and also Edwin West."