The Enchanted Buffalo (A Prairie Tale) by L. Frank Baum
The seven hundred bison of the Royal Tribe of Okolom dominate the Great Plains; even the Indian hunters do not molest them. They were ruled for many years by their majestic King Dakt; but in time Dakt grew old. One day, the tribe notes the absence of the king; they send Barrag, a powerful bull, back along their course to search. Barrag returns with news that Dakt is dead. One old bull notes that Barrag has failed to wipe the blood off his horns as thoroughly as he might have done.
Barrag claims the kingship. He is challenged by four other bulls, but defeats each challenger in turn. When he thinks that he has secured the crown, one more challenger arises: it is Oknu, the half-grown son of the late Dakt. The elder bulls will not permit a combat until Oknu is fully grown.
That night, as the herd sleeps, Barrag sets out alone across the prairie. In time he reaches an outcropping of rock, large and forboding; he enters a crevasse, and soon meets Pagshat, the Evil Genius of the Prairies. From their talk, it is clear that Barrag is a supplicant and client to Pagshat; the Genius has given the bison the strength of ten and made him king of the Okolom. Barrag complains of the upstart Oknu; Pagshat gives the bull a magic charm to enchant Oknu into any animal form he chooses.
On the way back to the herd, Barrag crosses paths with a black panther, and easily crushes the cat's skull with his hoof. He feels contempt for the dead beast. Back at the herd, Barrag works the magic spell; but he unwisely transforms Oknu into a black panther.
The astonished herd watches as the panther springs on Barrag's back and digs his teeth and claws into the bull's flesh. Barrag does everything he can to shake the panther off him, with no success. Desperate, Barrag races away across the plain, the panther still clinging to him. The bull runs long and hard, southward through the territories of the Ute, the Apache, and the Comanche; vultures and jackals observe him. For a time it seems that Pagshat runs alongside him — but cannot or will not help Barrag further.
Inevitably, in the end, Barrag collapses from exhaustion. Once the usurper is dead, the magic spell dissipates and Oknu returns to his proper form. It takes the young bull a full year to find his herd again. Once re-united with them, he reigns as the unchallenged heir to his father Dakt, ruler of the Tribe of Okolom.