When I was first learning about dogs from my mentor, he taught me that a dog's temperament is based on their "prey threshold" i.e. what types of prey they are genetically programmed to hunt. So bird dogs have a certain temperament because they are tuned to birds (soft mouth). And you can imagine a bulldog, grabbing and holding onto the bull (hard mouth) and what kind of temperament and drive is required of that particular dog. And so on and so forth, in this way we account for all the different types of hunting dogs and their different types of prey, and that is what tunes the dog's nervous system and gives you an idea of how their personality will turn out.
To me, personality emerges as a process. Over time, the template of the inborn temperament interacts with the environment and this is what creates personality.
Nature (Temperament) + Nurture (Environment + Experiences) = Personality
But then there are other aspects of temperament as well, such as sensitivity to outside threats (out group vs. in group). Think of personal protection dogs, herding dogs, or livestock guarding breeds. One of my favorite people to learn from, Dr. Stephen Porges, described this threshold, based on what roles certain breeds were developed for: "Different breeds have different 'temperaments' which are different thresholds to detect threat... We have to understand the roles that dogs have played during the evolution of human civilization. They've played different roles, and those roles are now locked into the genetics of these different breeds. A dog isn't just a dog. Dogs are nervous systems that have ranges of thresholds that react to threat cues."
This is very interesting!!! We can look at many aspects of a dog's "personality" (which is often used interchangeably with the term temperament), and see that they have different thresholds in different areas of life. Prey Drive and Threat Detection would be two of the most important aspects which will create the template for your dog's behavior.
Thinking about this will help you determine what kind of dog will best suit your lifestyle and living arrangements.