: a person who has very strong feelings about something (such as religion or politics) and who wants other people to have those feelings : a zealous person
A great way to spice up any story is to make your villain some kind of zealot who pushes himself on the protagonist and other hero characters. Even more appealing is the idea of a villain that is a zealous person who is powerful enough to penetrate the most secret of circles. An intelligent and ruthless villain completely filled with evil can open up so many story lines.
A zealous person generally develops as such over the course of time. There are many options for a back story on a zealous villain that can be used to build the worlds you are creating. Especially cool are the protagonist and villain growing up as friends and then being split due to the evil that grows in the villain. Obi-Wan and Anakin; HAL and Dave; Joanie and Cha-Chi.
I imagine there are equally zealous scientists in their respective fields. Those working tirelessly on their experiments and trying to recruit young scientists to their cause. No shortage of evil out there but for the most part, I believe science is a noble pursuit. Mankind is ultimately better because of their pursuits and we should all be thankful for their work.
Thank you all for reading during the 2014 A to Z Challenge and I look forward to reading your prose and wisdom on this writing journey.