Ujvcas, a North American Indian, sachem of the Mohegan tribe in Connecticut, died about 1682, at a great age. He was originally a war chief of the Pequot nation, but about 1635 revolted from the Pequot sachem Sassacus, and gathered a band of Indians who were known by the old title of Mohegans once borne by the Pequots. In May, 1637, he joined the English in the war against the Pequots, and proved a valuable auxiliary, receiving for his services another portion of the Pequot lands. Many of the Pequots were shielded by him from the vengeance of the English when the war was over, and for this he was for a time in partial disgrace with the authorities; but he was soon received again into so great favor with the whites that several attempts were made by different Indians to assassinate him. Uncas accordingly attacked and reduced Sequasson, sachem of the Connecticut river, and in 1643 defeated and took the powerful Narragansett sachem Miantonomoh, whom he finally put to death. He was a brave but tyrannical chief, and frequent complaints were made to the colonial government of his oppression. In 1648 the Mohawks, Pocomtocks, and other tribes made war against Uncas with but little success.

He was besieged in 1657 in his stronghold on the Connecticut by the Narragansett chief Pessacus, and nearly starved out; but he was relieved at almost the last moment by Ensign Leffingwell, who took in to him at night a canoe laden with supplies. For this act, it is said, Uncas gave to Leffingwell a deed for all the land upon which the town of Norwich now stands, though that chief afterward sold it to a company. He was characterized in 1674 as "an old and wicked, wilful man, a drunkard, and otherwise very vicious; who hath always been an opposer and underminer of praying to God." He was the ally of the English in all their wars against the Indians.