The most important traits in any career is the desire and will to pursue and excel within it. It can be argued that certain personal qualities are more or less valuable to a scientist, but any such list will always be subjective. The best that can be done is to find some commonalities in the skills and environment across varied scientific disciplines and determine what qualities may be best suited to those skills and surroundings.
The scientific method is a system of asking questions, making speculations, observing and drawing conclusions; a method applied in some form or another to most scientific fields. To this end, scientists who are naturally inquisitive have an advantage, as they will, in a sense, apply the scientific method to what they see and observe with little prompting. Whether an astronomer behind a telescope or a biologist in the field, an inclination to ask questions about observations can only help in scientific pursuits, especially when questions lead to further questions and begin opening up new avenues of investigation.
An analytical mind is a boon to a scientist of any discipline. Scientists often work with large amounts of collected data and, especially in fields such as physics and atmospheric science, they must also contend with complex mathematical equations on a regular basis. The ability to correlate data accurately, draw reasonable conclusions and avoid errors in calculations is vital for a scientist. Inaccuracies or findings based in unsound science can have far-reaching consequences, especially among those who may be called to predict likely outcomes based on their data and calculations, such as meteorologists and astronomers.
Most scientists work as a team at least part of the time, making cooperation and interpersonal skills necessary for success. Some scientists, such as meteorologists and zoologists, additionally have frequent cause to interact with the public, making communication skills of even higher priority. Cooperation, effective communication, and the ability to work toward a common goal with others represent a suite of traits necessary for all scientists to share. Without it, large projects and correlating shared data across disciplines becomes much harder.
Creativity is not always considered among the traits a scientist needs, but its importance should not be underestimated. The purpose of scientists is to confront very large and complex problems, and it takes a creative mind to extrapolate solutions from gathered data, research and experimentation. This may take many forms: finding a way for humans to coexist peacefully with an endangered habitat; making an intuitive leap in understanding the significance of a new space anomaly; conceiving a new method of utilizing an underused chemical material; or many other out-of-the-box solutions scientists have created over the centuries. It is difficult to gauge or quantify this sort of inspiration, but when it appears, it is among the most valuable of a scientist's traits.