Because his nose lights the way...
Rudolph
Santa needed Rudolph the Red-Nosed Reindeer to lead due to his glowing nose. It helped them make it through the heavy fog.
Yes, Rudolph is Santa's main raindeer!
rudolph Rudolf
Oh my! Why would Santa ever do that! Rudolph is Santa's most trusted guide. With Rudolph's nose shining "so bright", Santa won't lose his way. No, no Santa would never get rid of Rudolph. Besides, it would break Rudolph's heart.
Santa used Rudolph when it was foggy and he needed help seeing. Now Rudolph comes along just in case.
Rudolph does not get sick.
Rudolph is a fictional reindeer that helps to pull the sled of Santa Claus. It is said that Rudolph can fly and has a bright red nose that helps Santa navigate in bad climactic conditions.
Santa needed Rudolph because of his glowing red nose. It helped guide Santa's sleigh through a storm, and saved Christmas.
Rudolph's Dixon Nixon
Rudolph.
Santa picked Rudolph because he had a nice shiny nose that would help him see through the fog.