I've heard it claimed that the expression "Shimshon HaGibor" (Samson the Mighty) [as a descriptive of Shimshon in Tanach] was invented by the Zionists, to promote their "strong Jew" narrative. Is this true?
Firstly, the צמח דוד, referred to in another answer, was actually first printed in 1592. Secondly, the first source I've found is מכילתא דרבי ישמעאל; the term can also be found in סמ"ג, in ספר חסידים, in Maharsha, and in numerous other seforim.
On the other hand, the incidence of this term is not particularly frequent. If we replace 'Zionism' with 'Modern Hebrew Literature' which is commonly said to have begun in the mid-1700s, it is quite plausible that this might have done much more than the handful of traditional sources to popularize the term. Conversely, the term may always have been more common in the vernacular as opposed to formal, religious writing, and it might have been only the modern Hebrew books which adapted it as a preferred literary appellation.
The phrase 'Shimshon Hagibor' goes back to the 12th century in northern france in the peirush on Genesis 49 17a peirush identified with 'Rabeinu Tam' [Published by Avraham Shoshana 2017]. It appears in Sefer Chasidim 12th century as well. shortly afterwards appears in the Halachic book סמ"ג. Its Known that 'Hagibor' was attached to rabbi Shimshon of Metz, a Famous Tosafit in northern france.
The combination of Shimshon hagibor was common in Ashkenaz, and can barely be found in Jewish writings from Spain. [By the the way, in some versions of the Mechilta on Beshalach from first centuries this phrase appears but is most likely a typo, for it does not appear in any significant manuscript....].
Interesting point is that in the writings of Hamza al-isfahani [Islam 10th century] he appears as 'al jabar' [Hagibor]. Since all information about the Judges in muslim writings came from Jewish sources- this points at very early stages of appearance in jewish thought.
One more significant source is the Targum Yonatan Ben Uziel on Jeremia 9 22 who ties between Hagibor and Samson. The whole idea as if Zionism 'Invented' the concept of Jewish Heroism is close to absurd and many times based on pure ignorance. Its enough to read the Bible and understand the value given to Physical heroism [For instance the long lists of davids heroes in Samuel b 23, Davids wars and his lament over saul and Jonathan etc...].
The rumor is false. The earliest I can find the phrase 'Shimshon HaGibur' goes back to 1831, long before modern zionism or Hertzl.
It can be found in the book צמח דוד
Google books also shows other phrases such as Shimshon our Hero from books in 1801, but those are in English and not the exact phrase. I would not be surprised to find it occurring even earlier than that.