Ares: Ares is the Greek God of war and the son of the God Zeus. He is the major enemy of Wonder Woman, who had many conflicts with her and hundreds of times he tried to disturb the peace in the world. Every once in a while he tries to cause assaults but each time Wonder Woman defeats him and reestablishes peace. Ares first appeared in the very first issue of Wonder Woman itself and in the pre crisis episodes he was referred to as Mars.

Baroness Paula Von Gunther: She is the arch enemy of Wonder Woman, an evil scientist, a ruthless spymaster of Nazi spies and a fatal female. She fought many battles against Wonder Woman but later Diana discovered that Paula’s Daughter was kidnapped and held hostage by Nazis and thus they forced Paula to work for them. Wonder Woman rescued the girl and the Baroness Paula happily helped Diana against Nazis after that.
Cheetah: Priscilla Rich was the original Cheetah who wore a cheetah skin costume and took a vow to destroy the Wonder Woman. Debbi Domaine, the niece of Priscilla, was the second Cheetah in pre crisis stories. She was an ecologist but later she was kidnapped and made an eco-terrorist. Barbara Minerva is the latest cheetah, who was an archeologist and a treasure hunter. But, then she sold her soul to Urtzkartaga, a plant God who is also the God of immortality and power, and became his eternal servant.
Circe: Circe was a deadly witch and a wizard with vast power who had specialized in transforming spells and illusions. She appeared in 37th issue of Wonder Woman and she is one of the most dangerous enemies of Diana.
Cyborgirl: Sarah Charles, the maintainer of super-hero Cyborg’s cybernetic components was Cyborgirl’s aunt. So, she implanted some of the cybernetic components to Cyborgirl’s body and made her powerful. Instead of using the powers for good, Cyborgirl decided to fulfill her selfish motives and thus became a villain and an enemy of Wonder Woman. 
Doctor Cyber: She is the head of an international crime association and a criminal mastermind. When Wonder Woman had given up all her powers and became a simple karate expert, Doctor Cyber was her formidable enemy. In a fight, Cyber’s face was burnt so she vowed to avenge Diana by ruining her face. She also made friends with Doctor Moon, an enemy of Batman.
Duke of Deception: Duke of Deception is Ares’s servant and Wonder Woman’s old enemy. He embodies confusion, treachery and deceit and uses his powers of shape shifting, illusion and influencing minds to cause wars. He even plagued Wonder Woman’s thoughts.
The Mask: Nina Close, an oppressed and frail wife of a billionaire industrialist developed a problem of insanity and split personality. She wore a mask that would dispense a poisonous gas; hydro-cyano , if not removed properly. Once, Nina also stole Wonder Woman’s invisible jet.
Shim'Tar: She was a champion from an Amazon tribe Bana-Mighdall, who wore an armor which was empowered by the golden girdle of Gaea. She wanted to use it to kill Wonder Woman and take over the tribe; Bana-Mighdall, but Diana took the girdle off her and she died. Later, during the War of Gods, second Shim’Tar was formed.
Zara: Zara, a pyrotechnics expert was a leader of the Crimson Flame cult. She was sold into slavery when she was a child and had to face many horrors in her life. She hated mankind and when Wonder Woman defeated her cult, she joined another group the ‘Villainy Inc’; enemies of Wonder Woman. Zara tried to avenge Wonder Woman as well as her mother Hippolyta.
Apart from these, other major enemies of Wonder Woman are; Angle Man, Blue Snowman, Dark Angel, Decay, Devastation, Doctor Poison, Doctor Psycho, Eviless, Genocide, Giganta, Hypnota, Julianna Sazia, Maxwell Lord, Osira, Queen Clea, Silver Swan, Tezcatlipoca and White Magician.