towering like a mountain and calm like a spring; describes a person of great dignity and composed character

To stand tall like a mountain and be deep like a pool; describes someone with noble character and a steady, dignified presence.

having a dignified and steady presence like deep waters and high mountains

(idiom) to have a serene yet formidable demeanor; to have a commanding presence, literally "deep as a pool and still as a mountain"

deep and stable like water in a pool or a towering mountain; describes someone with a dignified and imposing demeanor