Here is the story of Alexander and Bucephalus

In fact, this combination of a calm and calculating thoughtfulness, with the ardor and energy which formed the basis of his character, was one great secret of  Alexander’s success. The story of Bucephalus, his famous horse, illustrates this in a very striking manner. This animal was a war-horse of very spirited character, which had been sent as a present to Philip while Alexander was young. They took the horse out into one of the parks connected with the palace, and the king, together with many of his courtiers, went out to view him. The horse pranced about in a very furious manner, and seemed entirely unmanageable. No one dared to mount him. Philip, instead of being gratified at the present, was rather disposed to be displeased that they had sent him an animal of so fiery and apparently vicious a nature that nobody dared to attempt to subdue him.

In the mean time, while all the other by-standers were joining in the general condemnation of the horse, Alexander stood quietly by, watching his motions, and attentively studying his character. He perceived that a part of the difficulty was caused by the agitations which the horse experienced in so strange and new a scene, and that he appeared, also, to be somewhat frightened by his own shadow, which happened at that time to be thrown very strongly and distinctly upon the ground. He saw other indications, also, that the high excitement which the horse felt was not viciousness, but the excess of noble and generous impulses. It was courage, ardor, and the consciousness of great nervous and muscular power.

Philip had decided that the horse was useless, and had given orders to have him sent back to Thessaly, whence he came. Alexander was very much concerned at the prospect of losing so fine an animal. He begged his father to allow him to make the experiment of mounting him. Philip at first refused, thinking it very presumptuous for such a youth to attempt to subdue an animal so vicious that all his experienced horsemen and grooms condemned him; however, he at length consented. Alexander went up to the horse and took hold of his bridle. He patted him upon the neck, and soothed him with his voice, showing, at the same time, by his easy and unconcerned manner, that he was not in the least afraid of him. A spirited horse knows immediately when any one approaches him in a timid or cautious manner. He appears to look with contempt on such a master, and to determine not to submit to him. On the contrary, horses seem to love to yield obedience to man, when the individual who exacts the obedience possesses those qualities of coolness and courage which their instincts enable them to appreciate.

 At any rate, Bucephalus was calmed and subdued by the presence of Alexander. He allowed himself to be caressed. Alexander turned his head in such a direction as to prevent his seeing his shadow. He quietly and gently laid off a sort of cloak which he wore, and sprang upon the horse’s back. Then, instead of attempting to restrain him, and worrying and checking him by useless efforts to hold him in, he gave him the rein freely, and animated and encouraged him with his voice, so that the horse flew across the plains at the top of his speed, the king and the courtiers looking on, at first with fear and trembling, but soon afterward with feelings of the greatest admiration and pleasure. After the horse had satisfied himself with his run it was easy to rein him in, and Alexander returned with him in safety to the king. The courtiers overwhelmed him with their praises and congratulations. Philip commended him very highly: he told him that he deserved a larger kingdom than Macedon to govern.>>