"Hit me with the very best shot you've got!"—Tuxedo Mask, episode 73
Tuxedo Mask...the classic male hero who is very very cute and helps his fair lady whenever she's in trouble. In many ways, he's Serena's knight in shining armor. But instead of a sword, he's armed with a cane and roses. He appears usually at the most dire moment of the battle, standing on something like a streetlight. One can always tell he's arrived when a rose hits the ground from the sky at high speed. (For a short period of time, he was also the Moonlight Knight.)
He has a henshin, I don't think it has a name. Here's a pic of it:
As for attacks, the question is, does he really have any? Not that I've seen. Not unless you call throwing roses and twirling a cane attacks.
Who was Darien during the Silver Millenium? He was Prince Endymion, the Earth's prince and guardian. This fits perfectly with his Japanese name, Chiba Mamoru. Chiba in this case is written in kanji, and means "earth", and the Japanese word "mamoru" means "protector". He and Princess Serenity fell in love back then, but this was forbidden. Lots of problems there, of course. Like the Princess, he had four protectors: Zoisite, Kunzite, Jedite, and Nephrite (all of which, more or less, are now villains). His palace was at a place called Elysion.
As a civilian, he is known as Darien (Darien Shields in the manga), Serena's tall, black-haired and really cute boyfriend. He is the father of Rini and the future King Endymion of Crystal Tokyo. His parents died in a car accident when he was very young. He had to go to a hospital (I think) around that time, and he met a boy named Fiore there. That is also where he met Serena. Since he was released, he's lived on his own. He's probably older by about 2-3 years. He's good friends with Andrew, who works at the arcade (and who Serena likes a bit).