Analysis of information sources in references of the Wikipedia article "Dungeons & Dragons iconic characters" in English language version.
"So, one of the things that I thought a lot about when I was first putting together the outline for this book... this is not the core Monster Manual.... So, there are some monsters that I very intentionally left out of this book so that when they appear in Monster Manual II, that will help communicate, "Hey, look, this is a core Monster Manual." You don't have frost giants if you don't have Monster Manual N".
"So, one of the things that I thought a lot about when I was first putting together the outline for this book... this is not the core Monster Manual.... So, there are some monsters that I very intentionally left out of this book so that when they appear in Monster Manual II, that will help communicate, "Hey, look, this is a core Monster Manual." You don't have frost giants if you don't have Monster Manual N".