Gandalf the Gray

Five great wizards (Istari) came to Middle-earth for protection and training:
Saruman the White (aka Kurumo or Kurunir, mired in politics and was eventually destroyed).
Gandalf the Gray (aka Olorin or Mithrandir, a wandering wizard, after falling into the Abyss, returned and replaced Saruman, taking on white).
Radagast Brown (aka Ayvendil, took care of all forest creatures, large and small).
Two "blue magicians" (Alatar and Pallando), shortly after the arrival of those who left to the east (hypothetically, they "took up" the wild tribes and distant territories of Middle-earth).
There were others, but these five are the most powerful.