The melody is attributed to the renowned Tzadik known as the Shpoler Zeideh (the grandpa from Shpoleh).
The background to this melody according to Chassidic tradition has the following story:
The nobles ruling the villages in old Russia and Ukraine in those days, used to make sport on the Jews subject to them, by dressing them up in bearskins and forcing them to dance with a Cossack. When the Jew failed to keep step with the tune, he would suffer lashes with the whip.
Once a Jew who had rented an estate from the noble was imprisoned for failing to pay his rent on time. When his turn came to dance in the bearskin, the Shpoler Zeideh managed to take his place and perform the dance for him which culminated in the Zeideh's gaining the upper hand over the Cossack.
This melody gives expression to this incident and for this reason opens slowly, gradually working to a climax in the light of the dancer's success and the defeat of the Cossack opponent. It therefore ends with a cry: "Hopp Cossack!" The song is meant as a spur to fervent and joyous worship of G‑d. It is sung on joyous occasions, on Simchat Torah and the like.
It's said that the Shpoler Zeideh learned the dance from Eliyahu Hanavi (Elijah the Prophet). And for years afterwards he danced this dance every Motzei Shabbos.
By the Rebbe