Artemis

Artemis was a talking cat and advisor to Minako Aino/Mina Aino. He awakened Minako as Sailor V before Usagi was awakened as Sailor Moon. Artemis and his partner Luna were advisors to Queen Serenity in the Silver Millennium, and when the kingdom was ruined, Serenity used the power of her Silver Crystal to send the two cats to Earth's future in order to awaken the Sailor Senshi.

Anime
In the anime, Artemis was more emotional than in the manga, with an occasional clumsy streak. He hardly ever became angry with Minako, though he did criticize her personal life quite a bit. Their relationship almost seemed to be that of sister and brother. Artemis also encouraged Minako to pursue her dream of becoming an idol.

He was not shown to have a very strong relationship with the other Senshi, but when Diana appeared, he became very emotionally attached to her. Artemis also seemed to have more memory of their past in the Silver Millennium.

Artemis never took human form in the anime and Mau was never mentioned.

Manga
Compared to the anime, Artemis' character was very different in the manga. In Codename: Sailor V he was rather quiet, very critical, and sarcastic. Even in the Sailor Moon manga, when Luna fell in love with a man in "Kaguya-hime no Koibito," Artemis seemed oddly unmoved, more disappointed rather than upset. He also had a tendency to throw tantrums when Minako was acting too childish for his liking. Despite this the two became closer throughout the series, and in the final arc of Sailor V, Minako stated that he was her only true friend. In the Sailor Moon manga, Artemis and Minako were inseparable at first, and he appeared very proud of his ward. In the manga, Artemis and Luna were originally from the Planet Mau, and in times of crisis could take on human form (as could Diana) briefly. He did so during the Dream arc to stop Minako from falling off a crane while fighting the Amazoness Quartet. Also during the Dream arc, when Artemis peeked at Minako in the shower and noted that she was beginning to resemble Aphrodite, he became flustered, possibly due to a crush on Minako. Artemis was also instrumental in the awakening of Super Sailor Venus; he blamed himself for not having enough power and holding her back, but gave her the Venus Crystal. It was not revealed where he got it from, but it was strongly hinted that it was created out of the bond the two shared.

Despite any possibly romantic feelings for Minako, his true love was Luna. In fact, in the Sailor V manga, he fell in love with a dog, mistaking it for Luna.