One class of sacrifices is the chatat, the sin-offering. First the Torah tell us the general criteria obligating a chatat:
And Hashem spoke to Moshe, saying: Speak to the Children of Israel, saying, “A soul that sins unintentionally (BISHGAGAH), among any of the commandments of Hashem which shall not be done, and he commits one of these” (Vayikra 4:1-2).
From this we derive that a chatat is required:
If the sin was done in error (unintentionally).
For each commandment transgressed (among any of the commandments of Hashem).
For negative commandments that involve action, rather than speech (which shall not be done and he commits one of these).

Furthermore, only those sins that, had they been violated intentionally, carry a penalty of death-from-Heaven (karet), obligate a chatat if committed unintentionally, unless the Torah prescribes a different sacrifice. Rambam (Laws of Unintentional Sins, Chapter 1) enumerates 43 sins (23 of which concern sexual offenses) that necessitate a chatat.

The Torah then differentiates between chataot, based on the status of the one who committed the unintentional sin. There are four classifications:
If the anointed Kohen will sin to the guilt of the people, then he shall offer, for his sin that he committed, an unblemished bull to Hashem as a sin offering (v.3). …
And if all the community of Israel shall err (YISHGU), that a matter be hidden from the eyes of the congregation and they commit one of all the commandments of Hashem, which shall not be done, and they are guilty [this refers to the Sanhedrin giving an erroneous ruling and the people act accordingly]. And the sin that they committed becomes known; then the congregation shall offer a bull as a sin-offering, and they shall bring it before the Tent of Meeting (vs.13-14). …
When a ruler sins, and commits one from among all the commandments of Hashem that may not be done - unintentionally (BISHGAGAH) - and becomes guilty; or the sin that he committed became known to him, then he shall bring his sacrifice, an unblemished male goat (vs.22-23). …
And if an individual soul from among the people of the land sins unintentionally (BISHGAGAH), by committing one of the commandments of Hashem that may not be done, and he becomes guilty; or the sin that he committed becomes known to him, then he shall bring his sacrifice, an unblemished female goat, for the sin that he committed (vs.27-28). … If he shall bring a sheep as his sacrifice for a sin- offering, he shall bring an unblemished female (v.32). …
The exception to this is idolatry, which has its own sacrifice (see Bamidbar 15:22-29).

In enumerating the mitzvot, Rambam (Sefer HaMitzvot, introductory principle 7, “Not to count the details of the mitzvot separately”) explains that there is one mitzvah (positive § 69) regarding all individuals who commit a sin unintentionally, and a separate mitzvah (positive § 68) regarding the Sanhedrin.

The Torah’s order of these four classifications is striking. Clearly, the Torah places the leadership of the people before the layman, as Nehama Leibowitz writes:
“Since the greater the man, the greater his responsibility, each negligence, each slip of the mind, each indiscretion, each error on his part, borders on willful transgression. That is why we find a sliding scale of sin-offerings corresponding to the status of the person or body bringing it.”
However, what is the reason for the order among the leaders? Why does a group, the Sanhedrin, separate the two individuals mentioned, the Kohen Gadol and the ruler?

Sforno argues that the sins are listed in descending order of likelihood. In general, worthy leaders sin only because of the iniquity of the people, along the lines of:
“If one errs in his prayer, it is a bad sign for him; and if he is a prayer leader (shaliach tzibbur), it is a bad sign for those who sent him” (Berachot 34b).
The holiness and learning of the Kohen Gadol will usually keep him from even unintentional sins. And the ruler is listed last, because his very position of power makes him the most likely among leaders to sin.

Another approach is evident in Malbim, who differentiates between two words for “err”:
SH-G-G (BISHGAGAH) means an error in deed; for example, the person made a fire, thinking it was a weekday, and subsequently learned that it was Shabbat.
SH-G-H (YISHGU) means an error in judgment; for example, the person made a fire on Shabbat, unaware that it is forbidden, and then learns about the prohibition.
The passage opens with the criteria that apply in all four cases, including BISHGAGAH, that the sin was committed through an error in deed. The Torah repeats BISHGAGAH for the ruler and the layman, because theirs are, unquestionably, errors in deed. The error of the Sanhedrin (YISHGU), in contrast, is a mistaken legal ruling, which the people follow.

The error of the Kohen Gadol is also an error in judgment. He offers the specified sacrifice only if he is a sage worthy of rendering decisions (because he is equated with the Sanhedrin in Horayot 6b-7a), and he makes a mistaken ruling regarding himself and then acts accordingly. However, if his is an error of action, then he brings no sacrifice (Rambam, Laws of Unintentional Sins, 15:1-2).

Along the same lines, despite Rambam’s division of the Sanhedrin from individuals, Minchat Chinuch considers the chatat of the Kohen Gadol as part of the discussion about the Sanhedrin erring (§ 120), rather than in the discussion of individuals. The ruler is considered in the context of the individuals (§ 121).

By placing the Kohen Gadol apart from the ruler, and together with the Sanhedrin, the Torah communicates the unique status of the Kohen Gadol: he is more like the community than he is an individual.

In his person, even more so than the political ruler, the Kohen Gadol embodies and reflects the entire people of Israel.