He is one of the Iranian ancient myths. His story has been appeared in AVESTA book. In SHAHNAMEH (one of the main book of Iranians), in three places, name of ARASH, has been mentioned, but full story, you can`t find (first hand research). In PAHLAVI books (pre-Islamic period) and Islamic books, his name came in various articles.
ABOREIHAN BEIROUNI, in his book, ASARUL BAGHIYEH (remained effects), while describing the TIRGAN ceremony, is expressing the story of ARASH too. And believes that the root of this ceremony is from legendary which has been made by the said hero, some centuries ago. In AVESTA (religious book of Zoroastrians), ARASH, has called as EREKHSHE, and historians have brought many meanings for it, just like: bright, the person who has strong forearm, god of fast shooting arrow. In AVESTA, best shooter is mentioned as ARAKHSH, and it is guessed, that is ARASH. Some historians, believe was ruler of GORGAN area, who thrown away the Scythian tribe with the power of bow and arrow from border of Iran.

ARASH in cultural dictionary of DEHKHODA:

Name of hero, who was archer in division of MANOUCHEHR, the said ruler in last days of his ruling days, was forced to fight AFRASIYAB, in the beginning the victory was with AFRASIYAB, so MANOUCHEHR, took shelter in MAZANDARAN state.
But later both the rulers, decided about an Iranian brave man, who shoots and where ever that arrow lands, that place will be the border of Iran and TOURAN. ARASH thrown an arrow which moved from morning till afternoon and landed on JEYHOON River. So the said river assumed as the border. TABARI, named this archer as ARASH SHATIN, and NOLDEKE, assumes, this word, is the KHASHVOUEE ISHOU, which means, the god of fast shooting arrow, and this is a character or title of ARASH. And in another story, Vulcan (ESFANDARMAZ), gave the bow and arrow to ARASH, and told him this arrow is fast throw, but who throws it, dies on the spot. ARASH was aware of it and accepted the death. And thrown the arrow of ESFANDARMAZ, to develop the border of Iran (from the history of ancient Iran by HASAN PIRNIA).
As everything fell in the hand of destiny
Wisdom showed the policy
ARASH is a gem, but when, everything changes
He falls in battle of arrows (KHOSRAVI)
They call him ARASH the archer, because
From AMOL to MARV, he threw an arrow
You are suitable for ride, not ARASH
As you passed the SARI city for one hundred miles (VEIS and RAMIN)
And AFRASIYAB, attacked many times, and MANOUCHEHR, sent ZAL, many times to send the enemy to the other side of JEIHOUN, and again AFRASIYAB came with immense army and surrounded MANOUCHEHR in TABARESTAN area. At this time, SAM and ZAL were absent. So, at the end, for the sake of peace, they agreed to throw arrow.
ARASH, arrived with some soldiers and they called that border as TOURAN (MAJMAOL TAVARIKH).
Story of ARASH:
In the reign of MANOUCHEHR PISHDADI, in a war with TOURAN, AFRASIYAB, surrounded the soldiers of Iran in MAZANDARAN state, and finally MANOUCHEHR, proposed a peace and TOURANS, accepted the proposal. They agreed that, an Iranian archer, goes on the top of ALBORZ Mountain and throws an arrow, from the morning till evening, the arrow moved and by the side of JEIHOUN or AMU Sea, was landed on walnut tree. After this shooting, ARASH, dies of tiredness. ARASH, kept his life on the said arrow.
Many people, believe, ARASH is one of the unique samples in myths of the world. He is a symbol of sacrifice for the home land.
ARASH in recent literature:
*SIYAVASH KASRAEE, the Iranian poet has a poem by name, ARASH the archer
*TOURAN SHAHRIYARI, the Iranian poetess has a poem by name, ARASH and TIRGAN

Reference:

https://en.rasekhoon.net/article/show/1087361/ARASH-THE-ARCHER