Mallor was the third King of Arthedain. During his reign, or the end of his father's, the Istari first appeared in Middle-earth, shortly after the coming of the shadow to Greenwood. Around the same time, the Wise discovered that the source of the shadow was at Dol Guldur. Besides these discoveries, there was little strife during his reign.

Mallor reigned from TA 1027 until TA 1108, and died in TA 1110. He was succeeded by his son Celepharn.