The Orff are are a strange race. They are vaguely humanoid in shape, with three legs, and an exceedingly long neck. Their skin is perfectly clear, which makes the inner organs visible -- or rather, what is visible are mere distractions, false spots that draw attention away from the real or sensitive organs, and they have one internally huge eye - an eye whose pupil doesn't stay fixed in the center, but circles around the perimeter of the iris. They also talk quickly like the Garatrons, except they don't use thought-speak.
The Orff only appear once, in Book 41: The Familiar, which takes place in a false future where the Animorphs were discovered and the Yeerks took over the Earth and the Orff served as law enforcement. Since they are only seen in the future, it's assumed they recently became Controllers some point after Earth is captured.