According to the Mishna at the beginning of the perek, on daf 93b, the general rule is that a robber will have to pay back the victim according to the value of the object at the time that it was stolen.
Our Gemara presents a case where the ruling appears to be otherwise.
Once someone stole a set of oxen from his friend. He used them for a season of work, using them to plow his fields, to plant his crops, etc. At the end of the season, he returned the oxen to their true owner. When the case came before Rav Nahman, he ruled that the robber must return his profits from the harvest to the owner of the oxen, as well. In response to Rava’s objections that it was the field that increased in value, rather than the animals, Rav Nahman conceded that he would only have to share half of his profits. When Rava argues that the Mishna rules that the robber only has to return the stolen object in its original form, Rav Nahman became upset. He told Rava that he should not question his rulings, since Rav Huna has already compared him to Shevor Malka regarding these kinds of rulings. Furthermore, he explained, the robber in this case was a well-known criminal and he felt that he deserved to receive punishment for his actions.
Shevor Malka, or Shahpuhr, was the name of a number of Persian kings. Our Gemara is referring to the first King Shahpuhr, who continued his father’s success in wars against the Roman Empire, capturing the city of Netzivim and arriving at the border of Syria. In the course of a number of attacks, he not only defeated the Roman emperor Valerian, but he captured him and held him until his death. With regard to internal matters, he was an open-minded leader, and allowed a good deal of freedom of religion. It appears that he showed an interest in Judaism and was on good terms with the amora Shmuel. The simplest understanding of our Gemara is that Rav Huna compared Rav Nahman’s rulings to those of the ruling monarch.
According to Rashi, the comparison to Shevor Malka is not to be taken literally, and it is actually a reference to the Shmuel, whose rulings were accepted in monetary matters.