der Hecht
pike
A predatory fish that lives in freshwater lakes and rivers and is known for its long body and large mouth.
Der Angler war stolz auf den großen Hecht, den er gefangen hatte.
The angler was proud of the large pike he had caught.

pike
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pike
A predatory fish that lives in freshwater lakes and rivers and is known for its long body and large mouth.
Der Angler war stolz auf den großen Hecht, den er gefangen hatte.
The angler was proud of the large pike he had caught.

When referring to the fish, 'Hecht' (pike) is often combined with verbs such as 'einen Hecht fangen' (to catch a pike) or 'einen Hecht angeln' (to fish for a pike).
Mein Großvater hat früher oft Hechte geangelt.
My grandfather used to often fish for pike.
The idiom 'ein toller Hecht' is a fixed unit and is used colloquially for a man who is considered especially successful, brave, or attractive. It can be meant admiringly, but also slightly ironically.
Er prahlt ständig mit seinen Erfolgen, er ist schon ein toller Hecht.
He constantly brags about his successes; he really is quite the great guy.
In the meaning 'Sprung ins Wasser' (jump into the water), 'Hecht' (dive) is almost always used with a verb of movement. Typical phrases are 'einen Hecht machen' (to do a dive) or 'mit einem Hecht springen' (to jump with a dive).
Die Kinder machten am See einen Hecht nach dem anderen.
At the lake, the children did one dive after another.
hero
'der Held' and 'ein toller Hecht' can both refer to a man who seems impressive or gets attention from others. 'Held' is usually serious and positive when someone acts bravely or helpfully. But it can also be meant ironically when someone has done something stupid. 'Ein toller Hecht' is colloquial and often slightly ironic. It refers to a man who presents himself as strong, brave, or successful, sometimes also a bit boastful. The words can be confused because both can express praise. 'Held' fits real acts of courage, while 'toller Hecht' is more suited to a casual or ironic judgment of a person.

Nach seinem Sieg beim Turnier hielten ihn alle für einen tollen Hecht.
After his victory in the tournament, everyone thought he was a real great guy.
Der Lehrer nennt den Schüler einen Helden, weil er einem Mitschüler geholfen hat.
The teacher calls the student a hero because he helped a classmate.