Zahir was a Mikhal Traveler who caught Kes's interest and was attacked by the Doctor's dark alter ego.
Zahir was a member of the Mikhal Travelers, a group of wanderers who knew the region of space Voyager was passing through and offered to share what they knew. Charming and adventurous, he quickly drew Kes's attention, and she considered leaving Voyager to travel with him.
In The Darkling, the Doctor's experiments with adding traits of historical figures to his program produced a violent second personality. That dark persona saw Zahir as a threat, attacked him and then abducted Kes, threatening to throw her from a cliff before the crew intervened and restored the Doctor's original program.