1 Adar is the yahrzeit of Reb Avrohom ben Meir Ibn Ezra ZY"A. He is most famous for his commentary on Tanach. There is controversy over the philisophical aspects of his commentary. Reb Nachman of Breslov and others said one should not learn any commenteries based on philosophy. This does not detract from the righteousness of the authors. This was discussed on A Simple Jew. There are those who say that his students wrote the controversial parts.
Yahrzeit of the Shach, Reb Shabsei ben Meir HaKohen ZY"A. He is most famous for his commentary on Shulchon Aruch, Sifsei Kohen (Shach). See here for more info.