The German words for ambitious, in the sense of having a strong desire to succeed, are “ehrgeizig” (literally “greedy for honor”) and, more rarely, “ambitioniert”. In the sense of something being difficult to achieve (“demanding”), the German word is “anspruchsvoll” (literally “full of demand”). The nouns are “Ehrgeiz” (m.), “Ambition” (f.) and “Anspruch” (m.) (mainly meaning “claim”), respectively:

– “Er hat das Projekt voller Ehrgeiz begonnen.” – “He began the project full of ambition.”
– “Das war übertrieben ehrgeizig von dir.” – “That was overly ambitious of you.”
– “Diese Aufgabe ist sehr anspruchsvoll.” – “This task is very demanding.”
– “Er hat hohe Ambitionen (einmal) Chef zu werden.” – “He has high ambitions to become the boss (at some point).”