Shadal and R' Leone Da Modena
Shemuel David Luzzatto (1800-1865), known by his Hebrew acronym, 'Shadal' was an Orthodox Rabbi in Italy and a prolific writer, poet and scholar. While he supported the Wissenschaft des Judentums (science of Judaism) movement, he was a strict traditionalist who did not hesitate to attack Reform Judaism and its leaders with the harshest of terms (see later). I guess one can speculate that had he been alive today, he would have felt most comfortable in (a certain segment of) the Modern-Orthodox community.
Considering all of that, he should have naturally admired Rabbi Leone Da Modena of Venice (see previous post) and held him up as an early example of a "perfect maskil" , one possessing vast Torah knowledge as well as secular wisdom. Also, taking into consideration their similar views and backgrounds, the fact that they were both considered controversial by ultra-traditionalists and that they both held highly critical views of Kabballah and Zohar (in fact Shadal is credited for introducing a new rational anti-mystical approach to Judaism which had an indelible influence on Italian Jewry in the decades afterwards), an admiration for the man should have been a given, but instead Shadal held him in complete contempt.
The reason for this is that Shadal believed him (Da Modena) to be a hypocrite and a secret heretic(!).
To understand why, we need to discuss the curious case of the Sefer קול סכל Kol Sakhal. The book is an early anti-Rabbinic work whose author remains a mystery. There are differences of opinion among scholars about who the author could have been .
Shadal believed the author to be none other than Da Modena. What convinced him-beyond any doubt- that Da Modena was in fact the author of this book remains a mystery to me.
Shadal writes of him:
Have you seen שאגת אריה and קול סכל? Great novelty! It is clear beyond all doubt that קול סכל is also the work of Yehudah Aryeh Modena, and that this rabbi hated the sages of the Mishnah and the Talmud even more than the Karaites did, and that he was a bigger Reformer than Geiger! And this was 220 years ago! And in Italy!!
Should you copy it and bring it to the [Reform] Rabbinical Conference that will be held in Breslau, they will give you good money for it and will print it לְאוֹת לִבְנֵי־מֶרִי[from פרשת קרח: "a sign for the children of rebelliousness"] 
 It is interesting to note that both Shadal and Da Modena were descendants of Ashkenazic emigrants. The latter a descendant of Jews who were expelled from France and the former from Germany.
From the Jewish Encyclopedia:
According to a tradition communicated by S. D. Luzzatto (Shadal) the family descends from a German who immigrated into Italy from the province of Lausitz, and who was named after his native place ("Lausatia," "Lausiatus" = "Luzzatto"). The name "Luzzatti," which one branch of this family bears, can similarly be traced back to the plural form "Lausiati." The German rite is credibly reported to have been observed in the family synagogue (Scuola Luzzatto) in Venice.
 See Rivkin, Ellis. Leon da Modena and the Kol Sakhal (Hebrew Union College, 1952)
 Translated from the Hebrew in Talya Fishman, Shaking the Pillars of Exile: 'Voice of a Fool,' an Early Modern Jewish Critique of Rabbinic Culture (Stanford, 1997). See the original in 401 אגרות שד״ל, מס׳