Microorganisms thrive in almost every explored environment on Earth.  It is the almost that will be the primary focus of this talk; i.e., what prevents microbes from growing in those relatively rare sterile environments?  Answers to this question are required in order to make reasonable inferences about the nature of extraterrestrial life.  In this talk, a small cast of characters, consisting of the hardiest of known extreme microorganisms, will be introduced and described. The cast will be subjected, figuratively speaking, to an array of unforgiving physical and chemical challenges, culminating in the crowning of the ultimate “survivor”, the most extreme of the extremophiles.