Talmudic sources provide information about Shmuel HaKatan, presented as the author of Avot 4:19. He is also identified as compiler of Birkat HaMinim. Could he be the Tanna of both?
(יט) שְׁמוּאֵל הַקָּטָן אוֹמֵר, (משלי כד) בִּנְפֹל אוֹיִבְךָ אַל תִּשְׂמָח וּבִכָּשְׁלוֹ אַל יָגֵל לִבֶּךָ, פֶּן יִרְאֶה ה' וְרַע בְּעֵינָיו וְהֵשִׁיב מֵעָלָיו אַפּוֹ:
(19) Shmuel Hakatan said: “If your enemy falls, do not exult; if he trips, let your heart not rejoice, lest the Lord see it and be displeased, and avert his wrath from him” (Proverbs 24:17).
תָּנוּ רַבָּנַן: שִׁמְעוֹן הַפָּקוֹלִי הִסְדִּיר שְׁמוֹנֶה עֶשְׂרֵה בְּרָכוֹת לִפְנֵי רַבָּן גַּמְלִיאֵל עַל הַסֵּדֶר בְּיַבְנֶה.
אָמַר לָהֶם רַבָּן גַּמְלִיאֵל לַחֲכָמִים: כְּלוּם יֵשׁ אָדָם שֶׁיּוֹדֵעַ לְתַקֵּן בִּרְכַּת הַמִּינִים?
עָמַד שְׁמוּאֵל הַקָּטָן וְתִקְּנָהּ.
לְשָׁנָה אַחֶרֶת שְׁכָחָהּ, וְהִשְׁקִיף בָּהּ שְׁתַּיִם וְשָׁלֹשׁ שָׁעוֹת, וְלֹא הֶעֱלוּהוּ. אַמַּאי לֹא הֶעֱלוּהוּ?.... וְנֵיחוּשׁ דִּלְמָא הֲדַר בֵּיהּ....
שָׁאנֵי שְׁמוּאֵל הַקָּטָן דְּאַתְחֵיל בַּהּ. דְּאָמַר רַב יְהוּדָה אָמַר רַב, וְאִיתֵּימָא רַבִּי יְהוֹשֻׁעַ בֶּן לֵוִי: לֹא שָׁנוּ, אֶלָּא שֶׁלֹּא הִתְחִיל בָּהּ, אֲבָל הִתְחִיל בָּהּ — גּוֹמְרָהּ.
The Sages taught: Shimon HaPakuli arranged the eighteen blessings, already extant during the period of the Great Assembly, before Rabban Gamliel, the Nasi of the Sanhedrin, in order in Yavne. Rabban Gamliel said to the Sages: Is there any person who knows to institute the blessing of the heretics? Shmuel HaKatan stood and instituted it. The Gemara relates: The next year, when Shmuel HaKatan served as the prayer leader, he forgot that blessing, and scrutinized it, in an attempt to remember the blessing for two or three hours, and they did not remove him from serving as prayer leader. The Gemara asks: Why did they not remove him ...as we suspect that perhaps he is a heretic and intentionally omitted the blessing to avoid cursing himself. Shmuel HaKatan is different because he instituted this blessing and there is no suspicion of him....
The case of Shmuel HaKatan is different, as he began reciting the blessing of the heretics and while reciting it he became confused and forgot the end of the blessing. Consequently, he was not suspected of heretical leanings.
(א) וְלַמַּלְשִׁינִים אַל תְּהִי תִקְוָה וְכָל הָרִשְׁעָה כְּרֶֽגַע תֹּאבֵד וְכָל אֹיְבֶֽיךָ מְהֵרָה יִכָּרֵֽתוּ, וְהַזֵּדִים מְהֵרָה תְעַקֵּר וּתְשַׁבֵּר וּתְמַגֵּר וְתַכְנִֽיעַ בִּמְהֵרָה בְיָמֵֽינוּ:
בָּרוּךְ אַתָּה יְהֹוָה שׁוֹבֵר אֹיְ֒בִים וּמַכְנִֽיעַ זֵדִים:
(1) Let there be no hope for informers instantly perish; may all the enemies of Your people be swiftly cut off, and may You quickly uproot, crush, rout and subdue the insolent, speedily in our days. Blessed are You, Adonoy, Crusher of enemies. and Subduer of the insolent.
(כה) שמונה עשרה שאמרו חכמים כנגד שמונה עשרה אזכרות שבהבו לה' בני אלים. וכולל של מינים בשל פרושין, ושל גרים בשל זקנים, ושל דוד בירושלים. ואם אמר אלו לעצמן ואלו לעצמן יצא.
(25) Eighteen Berachot (blessings) that the Sages have established [for the prayer of Shemoneh Esreh have been established] corresponding to eighteen mentionings [of God’s name] that are in [the chapter of Tehillim that begins with] “Ascribe to God, children of princes…” (Tehillim 29).
And [a person] should include [the Beracha against] the heretics into [the Beracha] for the Rabbinical Jews, and [the Beracha] for the converts into [the Beracha] for the elders, and [the Beracha] for [King] David into [the Beracha] for [the rebuilding of] Jerusalem. But if he said each one of them separately he has fulfilled his obligation [of praying Shemoneh Esreh].
Issues that Prof. Ruth Langer cites in her article on "Birkat HaMinim:"
1) the late 1st century enactment by Rabban Gamliel is not attested in any historical source
2) a rabbinic council at that period would/could not enact a law/practice which would be adopted widely by other Jewish communities; such a legal structure did not become the norm until a few centuries later
3) the early Israelite-Christian community was not a concern for the rabbis to warrant a curse
4) the meaning of "Minim" in the widespread liturgy took on a meaning relative to the time (apostate, Hebrew-Christian, non-believer (Rambam), Sadducean, etc.
5) the earliest complete text of the Birkat HaMinim comes from the 10th century