Greg Marshall is an author whose specific identity may vary, as many individuals could have this common name. Without additional context, it is difficult to provide a short description of a specific Greg Marshall. It is possible to find a Greg Marshall who has written on various subjects ranging from marine biology to business practices, depending on their area of expertise. One Greg Marshall is known for his invention of the Crittercam, a device used to study animal behavior by attaching cameras to them in their natural environments. Another could be a writer specializing in marketing or sports. If you have a specific Greg Marshall or field in mind, please provide more details for a precise description.