der Lenker
handlebar
The bar with grips used to steer a bicycle, moped, or motorcycle.
Halte den Lenker mit beiden Händen fest, wenn du bergab fährst.
Hold the handlebar firmly with both hands when you ride downhill.

handlebar / driver / leader
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handlebar
The bar with grips used to steer a bicycle, moped, or motorcycle.
Halte den Lenker mit beiden Händen fest, wenn du bergab fährst.
Hold the handlebar firmly with both hands when you ride downhill.

The word 'Lenker' (handlebar / driver / leader) is derived from the verb 'lenken' (to steer, to guide). The ending '-er' can refer both to the tool for an action (the steering bar) and to the person who acts (the driver, the leader).
Er lenkte das Gespräch geschickt auf ein anderes Thema.
He skillfully steered the conversation to another topic.
The meaning becomes clear from the context. With a 'Fahrrad' (bicycle), it means the handlebar. With an 'Unfall' (accident), it means the driver. With 'Geschicke' (fate / affairs) or 'Politik' (politics), it means a leading figure.
Der Lenker des Fahrrads verlor die Kontrolle.
The rider of the bicycle lost control of the handlebar.
The term 'Lenker' (driver) for a driver is very formal. It is mainly used in official language, for example by the police or in news reports.
Die Polizei befragt den Lenker des Lastwagens.
The police are questioning the driver of the truck.
In a figurative, elevated meaning, 'Lenker' (leader / guiding force) describes a person who has great influence and steers the development of something, for example the 'Geschicke eines Landes' (the fate of a country).
Bismarck gilt als Lenker der deutschen Politik im 19. Jahrhundert.
Bismarck is considered a guiding force in German politics in the 19th century.
leader / conductor
'der Leiter' and 'der Lenker' can both mean a person who sets the direction. 'der Leiter' is the normal word for someone who leads a group, department, or organization. In this meaning, 'der Lenker' sounds more formal or figurative and refers to someone who strongly influences the development of something. Learners may confuse the words because 'leiten' and 'lenken' seem similar. For a normal leadership position, 'Leiter' is usually correct; 'Lenker' fits better in elevated or figurative texts.

In dem Artikel wird der Bürgermeister als Lenker der Stadtentwicklung beschrieben.
In the article, the mayor is described as the guiding force behind the city's development.
Wegen einer wichtigen Frage ruft Anna den Leiter der Abteilung an.
Because of an important question, Anna calls the department head.