Venus

What an example of how a character's history can be needlessly complicated? The Marvel Comic Venus is a prime example.
Golden Age

Golden Age Version

The originally Roman goddess Venus lived on the planet Venus. Bored by their life there, she ventured to Earth. She took the identity of Victoria Nutley Starr, who worked for Beauty magazine as an editor and journalist. However, she was also a superhero that fought supernatural threats like "Loki" (its unclear if this really is the actual Marvel Comics Loki or not). Her love interest was Whitney Hammond. Whitney and Della Mason (his secretary) doubted her claims that she is a god.
Agents of Atlas

Modern Age Incarnation

The character of Venus was unused until 2006 series Agent of Atlas. Instead of this simply being a continuation of the character, Venus' history was radically rewritten. The Golden Age Venus was revealed to be Aphrodite.
The modern "Venus" was actually a siren. The Ancient One was on a ship she attacked. He made "her soul as beautiful as her physical form" thus making her good. Upset by what she did, he went to a monastery until she accidentally used her powers and made the clergy lustful and was thus expelled. During years of wondering, she became convinced she was the goddess Venus and forgot the truth. Later, she joined Jimmy Woo's team of superhero G-Men, but the team only lasted six months before the government disbanded them. She took the human identity Vicki Starr. In the 1980s, she helped end a conflict between African tribes. In the 2000s, she joined the Agents of Atlas. Namora revealed the truth to Venus causing Venus to become depressed. However, Woo managed to help her regain her confidence and regain her forgotten powers. During Dark Reign, Venus helped fight against Norman Osborn. Despite Aphrodite originally wanting to punish her for "blasphemy", Venus managed to get Aphrodite to give her the title of the "goddess of love" via the beauty of her songs. Venus was a member of God Squad and helped stop the villain Amatsu-Mikaboshi.
Powers and Abilities
Being the daughter of the Phorcys (god of the deep seas), she has immortality and powers that allow her to function under water (such as super durability to withstand the pressure, breathing underwater, superhumanly fast swimming and so on). She is a skilled at learning new languages. Her "siren song" allows her to gain empathetic control of others. She can use for a variety of effect ranging from healing a broken spirit to manipulating the affected.
Due to being declared the goddess of love, she gained new powers. She has the powers of Olympians: super strength, agility and speed; dense body tissue, high speed flight, teleporting, empathy, turn invisible to humans, shape shifting and so on. She gained Aphrodite's girdle, which allows her make others nearby feel passion and lover and turn weapons into other objects that are not weapons.
References:
http://marvel.wikia.com/Venus_(Earth-616)
http://marvel.wikia.com/Aphrodite_Pandemos_(Earth-616)
http://www.comicvine.com/venus/4005-12632/
http://en.wikipedia.org/wiki/Phorcys