The cheetah runs fastest of all the animals.
The cheetah runs the fastest of all the animals.
I would think that only the first one is correct, but came across the same question where many people answered both were. Hadn't known about this rule. I look at it, the second, this way: The cheetah runs the fastest... . The fastest service company? runs the fastest what? hahaha 😀
You are correct. Â Probably the reason many think "the" should be included is that there are some constructions where "the" really should be included. Â In your example, "fastest" is an adverb modifying "runs". Â "The" needs to point at a noun and there is none so it is not needed. Â If you say, "The cheetah is the fastest runner of all the animals," both "the" and "fastest" modify the noun "runner" making this sentence correct. Â Sometimes people will shorten that sentence to say, "The cheetah is the fastest." Â Again "the" is before "fastest" but they both still modify "runner" (or "animal," or some other noun which is implied.)