Garuda was a legendary general in the Ancient wars. He may have been the king who rose against Master Moo at the beginning of the Anime series, stationed at the Phut Fortress, which would also make him Rio's father.
It was said that General Garuda had a special relationship with Suzaku, the Phoenix lord, and that the two protected one another. This would explain why the general had a special suit of armor fashioned to look like the Phoenix, likely imbued with Suzaku's own anima.
In the Anime[]
General Garuda is seen once in Episode 1 when Holly and Suezo are telling Genki the story of Moo's rise to power.