Lucifer, also known as the Morning Star and the Lightbringer, is associated with Venus, among other things. He is identified with the Greek Phosphoros and also with Eosphoros (frequently rendered Hesperos, or Vesper) who represented the Morning and Evening Stars. The two spirits were folded together when the Greeks figured out that the Morning Star and Evening Star where the same celestial body.
Contrary to popular misconception, he is NOT Satan. There is no biblical precedent for this, and in fact the only biblical instance of this name at all is simply one passage in Isaiah which was originally written "Morning Star" and referred to an ancient King who demanded that his subjects worship him as a Deity.
Personally, I love Lucifer. He's a great guy. Bit of a jerk, but I can respect that. I don't worship him, but I respect anyone who will stand up to God when they believe that He is wrong, even if I think he went about it in the wrong way. He's very clever, very insightful, and has a brilliant sense of humor if you get to know him. He's got a hell of an ego, and he won't tell an outright lie if he can avoid it. It's a matter of both pride and practicality: He doesn't need to -- the truth can be used to deceive far better than any lie under most circumstances. Also, a reputation for telling the truth is far more useful than a reputation as a liar. He's been viciously slandered by the Church for thousands of years, and the only way to fight that reputation is NEVER to be caught in a lie.
Like any powerful spirit, don't seek him out for foolish reasons. You're likely to contact a spirit impersonating him, or you may contact the real Lucifer but annoy him in the process. Neither of these scenarios ends well for you.