Nemesis is a name shared by two characters from the DC Universe.
Nemesis (Tom Tresser)
A government agent and master of disguise who pitted his skills against the evil Council after they brainwashed his brother Craig into joining them. He was later recruited into the second Suicide Squad, and came to love his teammate Nightshade. He eventually left the Suicide Squad to work on his own, and was seemingly slain while working undercover with Catwoman.
Nemesis' main weapons where his fighting skills and a special disguise method involving skin-adhering face-masks, which dissolved only under a special chemical spray.
Nemesis (Soseh Myrkos)
Created by the Council, Soseh Myrkos was a genetically engineered being, daughter of Dr. Anatol Myrkos. Artifically aged to adulthood, Soseh eventually turned on the Council, naming herself Nemesis, and was forced to slay her fraternal twin sister Ellina in one of her battles against the organization. Nemesis later teamed with the Justice Society of America to deal a crippling blow against the Council, but the Council was only totally destroyed when Black Adam slew all its members. Nemesis eventually joined a new force of warriors working for Black Adam, and helped them defeat the despot Asim Muhunnad, who ruled Adam's homeland of Kahndaq. While Adam's team acted as the new rulers of Khandaq, Nemesis entered a relationship with teammate Alex Montez, but was slain by Eclipso when he took Alex over.
Nemesis' chief power- besides her formidable combat skills- was an ability to copy any fighting technique she saw in action.