Luna

Luna is a talking cat and advisor to Usagi, it was she who first detected Usagi's power but did not at the time relise she was the Moon Princess. Luna and her partner Artemis 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 Soliders.

Luna awakened Ami, Rei, and Makoto to their identities as Sailor Soliders as well as awakening Usagi as Sailor Moon.

She and Artemis one day marry and have a daughter called Diana who becomes the advisor to Chibi-usa, Chibi-usa's toy Luna-P is also modelled on Luna.

Manga

In the manga Luna and Artemis are originally from the Planet Mau and in times of crisis can take on human form (as can Diana) briefly.

Anime

In the anime Luna only takes human form once, in the S Movie, and Mau is never mentioned.

Live Action

In the Live Action series, Luna is a talking and moving plush cat (not a real one) can become a human girl and transform into Sailor Luna to train and help the Sailor Soliders as a side-effect of being bathed in the light of the silver crystal. She turns back if she sneezes. Her powers have the elemental power of "candy" and she wields a large folding fan at times.