In English, as in German, there are various ways to describe a person who is intelligent, depending on whether you’re concerned with amount of knowledge, ingenuity, perception or judgement. While the main word is also “intelligent” in German, the following colorful words are more specific:

“klug” – This word is quite universal and can indicate a sharp mind, logical ability to think, educated, experienced, rational and sensible.

“schlau” – This word translates as “astute” or “smart” and is used for people who use available means creatively to reach their goals. Synonyms are “pfiffig” or “gewitzt”. A “smart alec” is “Schlauberger” (m.) or the pejorative “Klugscheißer” (m.) in German.

“helle” or “aufgeweckt” – These words (the former literally meaning “bright” and the latter “woken up”) are used to describe people (usually young people or children) who have a quick intellectual grasp of new concepts (for their age).

“kenntnisreich” or “sachkundig” – These words mean “knowledgeable” and “competent”.

“scharfsinnig” – This word means “perceptive” or “sharp”.

“gerissen” – This word has a negative connotation, literally means “ripped” and is used for people who know all the ropes so that they can’t be fooled by others, or who are clever in a way that serves their own interests.

Other words in this spectrum are “weise” (“wise”), “gescheit” (“brainy”/”intelligent”), “genial” (“brilliant”) and “clever” (“clever”). Relatedly, the figurative English “whiz kid” is a “Senkrechtstarter” (m.) in German, which literally means “something that takes off vertically”, like a rocket. A “genius” is “Genie” (n.), and a “prodigy”, of course, is “Wunderkind” (n.).