How do you say what's he like in French?

For physical descriptions, you could say Il est blond (he is blond), Il est grand (he is tall), or Il est petit (he is short). For other attributes, you could say Il est tres sympa (he is very nice), Il est assez penible (he is pretty annoying), or Il est adorable (he is adorable).

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If your question was to translate "What's he like?" in french, then Il est comment ? or A quoi il ressemble? would fit.