No one really knows. They were known to the ancient Greeks as Phosphorus (as the morning star), and Hesperus (as the evening star). Pythagoras is often credited with the observation that Phosphorus and Hesperus were a single body. He did that in the 6th Century BC.

Which Venus do you mean? The planet? Then the category "Literature" would not apply. 1) "Venus was known in the Hindu Jyotisha since early times as the planet Shukra. In the West, before the advent of the telescope, Venus was known only as a 'wandering star'. Several cultures historically held its appearances as a morning and evening star to be those of two separate bodies. Pythagoras is usually credited with recognizing in the sixth century BC that the morning and evening stars were a single body, though he thought that Venus orbited the Earth. When Galileo first observed the planet in the early 17th century, he found that it showed phases like the Moon's, varying from crescent to gibbous to full and vice versa. This could be possible only if Venus orbited the Sun, and this was among the first observations to clearly contradict the Ptolemaic geocentric model that the solar system was concentric and centered on the Earth." Source and further information: http://en.wikipedia.org/wiki/Venus#Studies_of_Venus 2) "It depends on what you mean by discover. Because Venus is so bright, the first caveman who went outside at dusk or dawn surely noticed it. The ancient Greeks knew enough about it to know that it was different from other "stars". Mercury, Mars, Jupiter, and Saturn were also known to the ancients. This probably includes among many others the Chinese, Babylonian, and early American cultures which were relatively sophisticated. Galileo in 1610 was first to observe that Venus had a visible disk and that it had phases like the moon so perhaps he could be considered to have discovered the modern Venus." Source and further information: http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/961205a.html 3) "Since Venus can be seen with the naked eye, no one really knows who discovered Venus." Source and further information: http://library.thinkquest.org/J0112188/venus.htm

1610 is the year T.A.S