Question

Who am I ?

A straight standing soldier,
From his crest to his toe,
Combating all darkness,
His primary foe.
Though 'tis unfair,
It's the profession he chose,
The longer he fights,
The shorter he grows.

Answer 1

Beef Eater

I hope this is your answer

it s just a try

Answer 2

The answer is a candle

As we light the candle it becomes shorter and shorter and it removes all the darkness.

Hope it helps you ....