And the name of the slain women was Cozbi the daughter of Tzur; he was the leader of peoples, of a Midyanite tribe.
Rashi makes the following observation. When the Passuk says 'he was the leader of peoples', it implies that Tzur was the King over more than just one Midyanite tribe, while when it says 'of a Midyanite tribe', it clearly implies that he was only king over one single tribe. Rashi thus understands it to mean that although he was indeed king over one individual tribe, nevertheless, because he was the most prominent of all the Midyanite kings, he was considered leader over all the tribes. Accordingly, Rashi says as follows.
אחד מחמשת מלכי מדין, את אוי ואת ראש אומות. רקם ואת צור וגו'. והוא היה חשוב מכולם, שנאמר ראש אמות. ולפי שנהג בזיון בעצמו להפקיר בתו, מנאו שלישי.
- He was the leader of peoples. He was one of five kings of Midyan, as the Passuk lists them, 'Evi, Rekem, Tzur, Chur and Reva the five kings of Midyan... But he was the most prominent of them all, as it says of him, 'he was the leader of peoples'. Nevertheless, because he had acted in a demeaning manner by casting his daughter loose to sin with others, the aforementioned Passuk lists him third.
This reflection is hard to understand, for if Tzur would have actually been demoted, then that indeed would have been a denigration to his status. But the Torah clearly states that he was not demoted whatsoever, rather he was still considered the most prominent of them all; in view of that, what defamation did he suffer when the Torah mentions him third, if in reality, he was still considered first and foremost?
There are three virtues through which one can earn the kingship. The most notable virtue is one's royal lineage, as through this, he naturally inherits the throne from his royal ancestors. Another notable virtue through which one can rightfully earn the kingship, is by means of one's wisdom, for although he cannot naturally inherit the throne, nevertheless, he is naturally worthy of the throne, for by the virtue of his wisdom he is fit to lead his people. The third and least worthy virtue through which one can earn the kingship, is through forcing one's way to the throne by means of his wealth.
This phenomenon of attaining the throne by means of this most unworthy virtue of one's wealth, is something that the Gemara in Megillah (יא ע"א) attributes to Achashverosh. The Gemara quotes the Passuk in Megillas Esther that describes Achashverosh as 'the one who ruled from Hodu to Cush', and then goes on to expound on the words 'who ruled', as follows.
המולך, אמר רב שמלך מעצמו. אמרי לה לשבח ואמרי לה לגנאי. אמרי לה לשבח דלא הוה איניש דחשיב למלכא כוותיה. ואמרי לה לגנאי דלא הוה חזי למלכותא וממונא יתירא הוא דיהב וקם.
- 'Who ruled'. Rav said: This teaches that Achashverosh did not inherit the throne by royal descent, rather ruled of his own accord. Some say that this is a praise of Achashverosh, for it implies that no one else was suited for the throne as he was. While others say that this is a disparagement of Achashverosh, because it means that he was not really fit for the throne but he paid an excessive amount of money to ascend to the position.
In view of this we can explain that Tzur was indeed the most prominent of the five kings, and thus the leader of all the Midyanite tribes. This was so, firstly, because his origin was royalty, and thus he naturally inherited his prominence and leadership. In addition, he was also exceptionally bright and intelligent, as well as extremely wealthy. As a result of these three virtues, he was indeed instinctively the most prominent of the kings, and a natural leader to all the Midyanite people. Nevertheless, after conducting himself in a most demeaning manner, behaving in a way which disparaged his royalty and intellect, he had practically lost the effect of those two virtues, and was left with only the third and least notable virtue, wealth, through with which he held onto his position and prominence.
When the Passuk lists him third, it isn't alluding to a demotion in his status and prominence, rather to a demotion to the foundation upon which he retained his prominence; which is the fact that he retained his position only by the means of the third and least notable virtue - that of his wealth.
זרע שמשון פרשתנו אות ג