Mizuno Ami, Sailormercury, is the quietest and least assertive of
the sailor senshi. After Sailormoon, she is the first of the senshi to regain her memories. However, she really doesn't play much of a main role after that.
This doesn't mean that she doesn't pull her own, though. She handles the technological aspects of the Sailors' fight for the good; she analyzes the weaknesses of the enemies and does a whole lot of fighting through the medium of technology.
Mizuno Ami has short blue hair and blue eyes, and is very smart - she has an IQ of 300, and is very confident in her intelligence and ability to succeed by her own merit. She seems to be rather detatched, with unexpected flashes of original humor. Her demeanor is very modest, earnest and thoughtful. She wants to grow up to be a doctor, like her mother, and studies very hard to achieve this goal. She is also very good at chess, a game which requires a great deal of analytical thought; in chess, she is the Japan junior champion. Her divorced father is a master painter, who taught her chess and swimming to calm herself. As with everything, Ami learned these lessons quite well; she also swims like a fish.
Ami-chan is pretty much a static character - her personality is pretty well formed at the beginning of the series, and stays that way. She is smart and dependable, and those qualities carry over to her persona of SailorMercury when she has to fight to protect the Moon Princess.
Sailormercury is, of course, the Princess Mercury, holder of the star seed of Planet Mercury. Regarding her name: "Mizuno" means water in Japanese, but I do not believe there is any specific Japanese equivalent of "Ami." It might be related to the French for "friend," though... which would make it "friend of water." If you translate each of the kanji seperately, the first character "a" can be translated as "Asia;" the second, "mi," means "beautiful." So Ami could also become "Asian Beauty of Water," which is quite poetic. (Thanks, Bunny!)
The translation of her name fits her senshi form, seeing as most of Sailormercury's attacks involve water, mist, snow, ice, or spray. (Attacks like "Aqua Mirage," "Shine Aqua Illusion," etc.) Also, Mercury's analytical skills make her indispensable to the team. She has a visor/computer thingy that maps out enemies and their weaknesses.
Ami-chan, then, is the quiet one. She's basically smart, caring, hard working, dependable, and lends stability to the group. (Trust me, they need it. With Usagi's flakiness, Rei's temper, Mako-chan's impulsive fighting spirit, and Minako's playfulness... they definitely need a large dose of Ami's stability.)
For more about Ami-chan: