WPA is WiFi Protected Access - it's the most common method of encryption used to secure a wireless network. If you have a laptop or smartphone and you're trying to connect to a WiFi network, you'll usually need to enter a WPA key (or password) in order to connect to it.
In the live-action adaptations by Sir Peter Jackson, Sauron is portrayed by Benedict Cumberbatch in The Hobbit trilogy (who also portrays Smaug in the same trilogy) and was played by Sala Baker and voiced by Alan Howard in The Lord of the Rings trilogy.
Other Maiar in the Lord of the Rings include the Wizards (Saruman, Gandalf, Radagast, and the Blue Wizards), the Balrogs, and, if you're into the Silmarillion, Melian. The reason Sauron stands out as more powerful is that Sauron took up with Morgoth, the Valar who went bad early on. Sauron became his most powerful and trusted lieutenant (save Gothmog, the Lord of the Balrogs), and probably learned much from his master.