Wikipedia
Manthor is a fictional character in J. R. R. Tolkien's Middle-earth legendarium, appearing in The War of the Jewels.
He was a lord of Men in the First Age. He was a descendant of Halmir of the House of Haleth; his parents were Meleth and Agathor, and his brother was Hunthor who fell in the ravine of Taeglin.
Manthor was the Master of the North-march of Brethil, a part of the forest by the River Sirion nearest to the Ford of Brithiach. He was akin to the House of Hador and took pride in this, and so was a supporter of Túrin Turambar. After the death of Brandir childless many of the Folk of Brethil wanted Manthor to become the Halad, for he was of the senior line - but by a daughter, and so by tradition his second cousin Hardang (of the male descent) was elected.
Hardang disliked Manthor and had no love for the House of Hador, so by his command Manthor became the Captain of the Guards at the Crossings of Taeglin. There the fear of the assault by Orcs was the greatest, and Manthor moreover was "the doughtiest man" among the Folk of Haleth. Among "his strong company" at the Crossings were Forhend, Avranc, and Sagroth. Manthor appointed his chief henchman Ebor to be the Captain of the Guards at Brithiach.
Nonetheless, Manthor desired Chieftainship, and when Húrin returned to Brethil and found his wife Morwen dying, the "shadow" of the Curse of Morgoth that followed him awoke Manthor's dormant ambitions. He perceived that Húrin had come with no good intentions, but used the fear surrounding his appearance to overthrow Hardang. Cunningly using the laws of Brethil, he summoned the Folkmoot where he accused the Halad of dishonouring the guest. Although Manthor had "a great natural concern for 'courtesy' - sc. civilized behaviour and mercy", he now in eloquent words set the people against Hardang and his following, the chief of whom was Avranc. This resulted in the burning of the Hall of the Chieftains and slaying of Hardang; Manthor tried to stop the Folk, but his attempts were futile.
The Folk wanted to elect Manthor the Halad, but two days after he himself was shot to death by Avranc, and thus through the shadow of Húrin ended the House of the Haleth. A new wave of fighting in the Obel Halad followed, and in the end Avranc was chosen the Chieftain by the small remnants of the Folk of Brethil.