Lord Hanuman is the son of Vayu Deva, the Wind God. Marut means Wind, and Maruti means “of the wind”, in this case it means “Son of the Wind”
Therefore Lord Hanuman is called Maruti.
Why he is called Hanuman as per scriptures
While still a baby, Hanumanji , the son of the wind god, tried to fly up and grab the Sun, which he mistook for a fruit. Indra, the king of the Gods, struck Hanumanji with a thunderbolt on the jaw (hanu), to stop Hanumanji. Thus he became known as Hanuman.
His original name is Anjaniputra ( his mothers name is Anjani) or Keshari Nandan ( his fathers name is Keshari).