Two+ Rav Kahanas
The other day, on Kiddushin 8a, we read about Rav Kahana:
לָא, לְעוֹלָם דְּלָא שָׁוֵי, וּכְגוֹן דְּקַבֵּיל כֹּהֵן עִילָּוֵיהּ. כִּי הָא דְּרַב כָּהֲנָא שָׁקֵיל סוּדָרָא מִבֵּי פִּדְיוֹן הַבֵּן, אָמַר (לֵיהּ): לְדִידִי חֲזֵי לִי חָמֵשׁ סְלָעִים.
The Gemara rejects this suggestion: No; actually, this is referring to a case where the calf or cloak is not worth five sela, and the latter clause is referring to a case where the priest accepted upon himself to value the items as though they were worth this amount, which is why the son is redeemed. This is like this incident in which Rav Kahana, who was a priest, took a cloth [sudara] from the house of a man obligated to perform the redemption of his firstborn son. Rav Kahana said to the man: For me, I view this cloth as though it were worth five sela.
אָמַר רַב אָשֵׁי: לָא אֲמַרַן אֶלָּא כְּגוֹן רַב כָּהֲנָא, דְּגַבְרָא רַבָּה הוּא וּמִבְּעֵי לֵיהּ סוּדָרָא אַרֵישֵׁיהּ, אֲבָל כּוּלֵּי עָלְמָא – לָא. כִּי הָא דְּמָר בַּר רַב אָשֵׁי זְבַן סוּדָרָא מֵאִימֵּיהּ דְּרָבָא מִקּוּבֵּי שָׁוֵי עַשְׂרָה בִּתְלֵיסַר.
Rav Ashi said: We said that it is possible to redeem one’s son in this manner only when the priest is an individual such as Rav Kahana, who is a great man and is required to wear a cloth on his head. It was common practice for important people to wear a scarf on their heads. But with regard to everyone else, i.e., those who do not wear these cloths and cannot say it is worth that amount to them, no, they may not perform the redemption of the firstborn son in this manner.
Tosafot note that the implication is that Rav Kahanah, as implied by his name, was a kohen, who could accept a pidyon haben.
רב כהנא שקל סודרא בפדיון הבן - משמע הכא דרב כהנא היה כהן ותימה דבסוף אלו עוברין (פסחים דף מט.) משמע דלא היה כהן דקאמר אי לאו דנסיבי כהנתא לא גלאי וי"ל דתרי רב כהנא הוו אי נמי י"ל דבשביל אשתו היה לוקח כדאשכחן בפרק הזרוע (חולין דף קלב.) רב כהנא אכל בשביל אשתו:
They point out that in Pesachim 49a, the implication is that he wasn’t a kohen, since he said “had I not married a kohenet I would not have been exiled.” And one could say that there were two Rav Kahanas. Alternatively, one could say that he took the pidyon haben based on being married to his kohenet wife, just as in Chullin 132a, Rav Kahana ate teruma based on his wife.
So firstly, yes, it makes sense that there are two Rav Kahanas. In Pesachim 49a, we read:
רַב אִידִי בַּר אָבִין נָסֵיב כָּהֵנְתָּא, נְפַקוּ מִינֵּיהּ תְּרֵי בְּנֵי סְמִיכִי: רַב שֵׁשֶׁת בְּרֵיהּ דְּרַב אִידִי, וְרַבִּי יְהוֹשֻׁעַ בְּרֵיהּ דְּרַב אִידִי. אָמַר רַב פָּפָּא: אִי לָא נָסֵיבְנָא כָּהֵנְתָּא, לָא אִיעַתַּרִי.
The Gemara also relates that Rav Idi bar Avin married a daughter of a priest. Two sons who were ordained to decide halakhic matters came from him, namely Rav Sheshet, son of Rav Idi, and Rabbi Yehoshua, son of Rav Idi. Similarly, Rav Pappa said: Had I not married a daughter of a priest, I would not have become wealthy.
אָמַר רַב כָּהֲנָא: אִי לָא נָסֵיבְנָא כָּהֵנְתָּא, לָא גְּלַאי. אֲמַרוּ לֵיהּ: וְהָא לִמְקוֹם תּוֹרָה גְּלֵית! לָא גְלַאי כִּדְגָלֵי אִינָשֵׁי.
On the other hand, Rav Kahana, who was not a priest, said: Had I not married a daughter of a priest, I would not have been exiled, as Rav Kahana was forced to flee from Babylonia to Eretz Yisrael. They said to him: But you were exiled to a place of Torah, which is not a punishment at all. He answered: I was not exiled as people are generally exiled, i.e., I did not emigrate of my own free will; rather, I was forced to flee from the authorities.
We know of Rav Kahana’s exile from Bava Kamma 117a. That story begins with:
הָהוּא גַּבְרָא דַּהֲוָה בָּעֵי אַחְווֹיֵי אַתִּיבְנָא דְחַבְרֵיהּ אֲתָא לְקַמֵּיהּ דְּרַב אֲמַר לֵיהּ לָא תַּחְוֵי וְלָא תַּחְוֵי אֲמַר לֵיהּ מַחְוֵינָא וּמַחְוֵינָא יָתֵיב רַב כָּהֲנָא קַמֵּיהּ דְּרַב שַׁמְטֵיהּ לְקוֹעֵיהּ מִינֵּיהּ
The Gemara relates another incident: There was a certain man who desired to show another individual’s straw to the gentile authorities, who would seize it. He came before Rav, who said to him: Do not show it and do not show it, i.e., you are absolutely prohibited from showing it. The man said to him: I will show it and I will show it, i.e., I will certainly show it. Rav Kahana was sitting before Rav, and, hearing the man’s disrespectful response, he dislodged the man’s neck from him, i.e., he broke his neck and killed him.
and later in the story:
אֲמַר לֵיהּ רַב כָּהֲנָא עַד הָאִידָּנָא הֲווֹ פָּרְסָאֵי דְּלָא קָפְדִי אַשְּׁפִיכוּת דָּמִים וְהַשְׁתָּא אִיכָּא יַוְונָאֵי דְּקָפְדוּ אַשְּׁפִיכוּת דָּמִים וְאָמְרִי מַרְדִּין מַרְדִּין קוּם סַק לְאַרְעָא דְיִשְׂרָאֵל וְקַבֵּיל עֲלָךְ דְּלָא תַּקְשֵׁי לְרַבִּי יוֹחָנָן שֶׁבַע שְׁנִין
Rav then said to Rav Kahana: Kahana, until now there were Persian rulers who were not particular about bloodshed. But now there are Greeks who are particular about bloodshed, and they will say: Murder [meradin], murder, and they will press charges against you. Therefore, get up and ascend to Eretz Yisrael to study there under Rabbi Yoḥanan, and accept upon yourself that you will not raise any difficulties to the statements of Rabbi Yoḥanan for seven years.
So the Rav Kahana who was exiled was in the days of Rav. He is presumably a first or second-generation Amora.
Meanwhile, there is a Rav Kahana who speaks to sixth-generation Rav Ashi, and cites Shmuel, in Berachot 24a:
אֲמַר לֵיהּ רַב כָּהֲנָא לְרַב אָשֵׁי: הָתָם אָמַר רָבָא: אַף עַל גַּב דִּתְיוּבְתָּא דִּשְׁמוּאֵל, הִלְכְתָא כְּווֹתֵיהּ דִּשְׁמוּאֵל. הָכָא מַאי? אֲמַר לֵיהּ: אַטּוּ כּוּלְּהוּ בַּחֲדָא מְחִתָא מְחִתִינְהוּ? אֶלָּא הֵיכָא דְּאִיתְּמַר — אִיתְּמַר, וְהֵיכָא דְּלָא אִיתְּמַר — לָא אִיתְּמַר.
Rav Kahana said to Rav Ashi: There, with regard to the law of phylacteries, Rava said: Despite a conclusive refutation of the opinion of Shmuel, the halakha is in accordance with the opinion of Shmuel. Here, what is the ruling? He said to him: Were all of them woven in the same act of weaving? Are there no distinctions between different cases? Rather, where it is stated, it is stated, and where it is not stated, it is not stated, and there is no comparison.
In our local gemara, it is Rav Ashi talking about Rav Kahana being a gavra rabba, so it makes sense that he’s talking about his contemporary, who was not exiled, and so may well have been a kohen.
By the way, that gemara in Chullin about Rav Kahana eating because of his wife also mentions many of the same characters, namely Rav Idi bar Avin and Rav Pappa.
רב כהנא אכל בשביל אשתו רב פפא אכל בשביל אשתו רב יימר אכל בשביל אשתו רב אידי בר אבין אכל בשביל אשתו
The Gemara relates that Rav Kahana, who was an Israelite, partook of gifts of the priesthood on account of his wife, who was the daughter of a priest. Similarly, Rav Pappa partook of gifts of the priesthood on account of his wife, Rav Yeimar partook of gifts on account of his wife, and Rav Idi bar Avin partook of them on account of his wife.
Tosafot there also discusses that there must have been two Rav Kahanas, with the one in Kiddushin being later.
רב כהנא אכל בשביל אשתו - זהו רב כהנא שגלה מבבל לא"י דפרק הגוזל בתרא (ב"ק דף קיז.) שלא היה כהן כדאמרינן בסוף אלו עוברין (פסחים דף מט.) אמר רב כהנא אי לאו דנסיבת כהנתא לא גלאי ואחר יש שהיה כהן בפ"ק דקדושין (דף ח.) רב כהנא שקל סודרא בפדיון הבן. [וע"ע תוס' קדושין ח. ד"ה ר"כ ותוס' ב"ב קי. ד"ה ולא ובפסחים מט: ד"ה אמר]:
In fact, there are more than two Rav Kahanas. The Wikipedia disambiguation page lists four, and I’ve seen a fifth as well. So too in Toledot Tannaim vaAmoraim.
So we are really dealing with Rav Kahana I, as well as Rav Kahana III or perhaps IV.