
das Wesen
nature
The inner character, fundamental nature, or true essence of a person, thing, or idea.
Trotz seiner rauen Schale hat er ein freundliches Wesen.
Despite his rough exterior, he has a friendly nature.
essence / being
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nature
The inner character, fundamental nature, or true essence of a person, thing, or idea.
Trotz seiner rauen Schale hat er ein freundliches Wesen.
Despite his rough exterior, he has a friendly nature.

being
A living being; a creature, whether a human, an animal, or a mythical figure.
In den Tiefen des Ozeans leben seltsame und unbekannte Wesen.
Strange and unknown beings live in the depths of the ocean.

system / sector
The entirety of the institutions, structures, and processes in a particular field, often as part of compounds such as 'Bildungswesen' (education system) or 'Gesundheitswesen' (healthcare system).
Er ist ein Experte für das gesamte Transport- und Verkehrswesen des Landes.
He is an expert on the country's entire transport and traffic system.
'Das Wesen' is closely related to the verb 'sein' (to be) (past participle: gewesen). It describes the essence, the way of being, or the existence of something or someone.
Das Wesen der Freundschaft ist Vertrauen.
The essence of friendship is trust.
You distinguish the meanings 'character' and 'living being' from the context. 'Das Wesen' as character describes a person's personality. 'Das Wesen' as a living being refers to a creature and is often used in the plural or in fantasy and science-fiction contexts.
Ihr ruhiges Wesen macht sie zu einer angenehmen Kollegin.
Her calm nature makes her a pleasant colleague.
To describe a person's character, 'Wesen' is often combined with an adjective. Common examples are 'ein freundliches Wesen' (a friendly nature), 'ein sanftes Wesen' (a gentle nature), or 'ein fröhliches Wesen haben' (to have a cheerful nature).
Der Hund hat ein sehr verspieltes Wesen.
The dog has a very playful nature.
In the meaning of 'system' or 'sector', 'Wesen' appears almost only as the second part of compound nouns (e.g. as '-wesen'). It then describes the entirety of all structures in a field.
Das deutsche Gesundheitswesen steht vor großen Herausforderungen.
The German healthcare system faces major challenges.
nature
Natur and Wesen can both refer to the fundamental nature of a person or thing. Natur tends to emphasize inherent or innate qualities, while Wesen focuses on the inner character or true essence. Use Natur for an inherent disposition and Wesen when the basic character is the focus.

Ihr freundliches Wesen macht den Umgang mit ihr angenehm.
Her friendly nature makes her pleasant to be around.
Aufgrund seiner ruhigen Natur arbeitet er auch unter Druck konzentriert.
Because of his calm nature, he remains focused even under pressure.