Much of this comes from my analysis of the character of Taiki, who is one of my favorite characters in all of anime. I did read some things into his personality, and I have role-played Taiki in the past, which I feel has allowed me to understand him better. If you disagree, you are welcome to do so. This is just how I happen to see Taiki as a Sailormoon fan. This is mostly based on the anime, where Taiki has a much larger role than the manga.
Name: Taiki Kou, aka Sailor Star Maker
Approximate Name Translation: "Atmospheric Light"
Birthday: May 30
Age: Sailorstarmaker's true age unknown, but Taiki Kou's apparent age is about 16
Astrological sign: Gemini
Blood type: AB
Favorite colors: purple, yellow
Hobbies: poetry, gardening, computers
Has trouble with: arguments, pushy fans, showing emotion
r Strongest point: intellectual mind and sharp memory
Weakest point: appears cold and uncaring
Responsibilities: guitar, keyboard, writing lyrics
Power: Star Gentle Uterus
Taiki Kou is by far the most serious of the Three Lights. His demeanor is usually cold and analytic, seeing the world in scientific terms. In his human form, Taiki is very studious, and often tied or beat Mizuno Ami in test scores. Although Ami (and all the inner senshi except Usagi, in fact) seems to have a crush on him, Taiki can't be bothered with such foolish romance, but he does eventually learn to respect her views. He was a member of the computer club and the gardening club at Juuban High School. He speaks eloquently and politely.
In his spare time, Taiki enjoys reading and writing poetry and tending to gardens. He dislikes the hordes of screaming Three Lights fans and cherishes his private, quiet time.
Cold enough to consider and make plans to use the sailor senshi of Earth to distract Galaxia's attention away from themselves and Kakyuu-hime, Taiki is truly the brains behind the Starlights, but he's not the leader that Seiya is. He dislikes Seiya's association with the other senshi, and argues with Seiya over many things, but when push comes to shove Taiki respects Seiya. As Sailorstarmaker, Kakyuu-hime comes first, her teammates second, and herself last. There doesn't seem to be much room for anything else in Maker's priority list, although she does later on come to respect the senshi of the Earth, and protect sSailormoon herself at the end. Loyalty is one of Maker's strongest points.
In both forms, Maker has a touch of a morbid sense about her in word and deed, and hope seems an alien concept to her (see the Blake poem Taiki recited to Makoto and Usagi). Maker takes no joy in fighting; she does it because she has to, to salvage the few precious things she has left: Kakyuu-hime, Fighter, and Healer. I also see Maker to be the maternal figure of the three; she is usually the one watching out for her teammates and trying to protect them (in both forms). She argues with her teammates from time to time, but it's in the same way that Rei and Usagi always argue: the arguments are born out of a close friendship and love.
As cold as Taiki is, however, there is room for him to open up and find hope. There are rare moments, few and far between, where a heart is shown beneath the icy demeanor. First, Usagi made him laugh (the first time "in ages", according to Yaten and Seiya). Then there's the trick he, Seiya, and Yaten tried to play on the inner senshi at camp, the card game at Usagi's house, and most importantly, when his heart was touched by a young girl in the hospital, who, whenever she heard the Three Lights sing, would see and draw an image of Kakyuu-hime. It almost seems that Taiki cuts himself off on purpose to avoid feeling pain, but every so often, something sneaks inside the wall and allows him a chance to open up to others.