“Chodesh Av,” the Month of Av, is referred to in the TORAH as the “Fifth Month,” counting from Nisan, the “First Month.” There is a Biblical reference in BaMidbar (33:38), where we find “And Aharon the Priest went up to Hor Hahar at the command of G-d, and he died there in the fortieth year after the Jewish People had left Egypt, in the fifth month, on the first of the month.” (BaMidbar 33:38). This is the only Yahrzeit mentioned in the Torah specifically with a date.

The kavana and permutation of Hashem's name which we have in mind during the blessing of the month on Rosh Hodesh in the Amidah of Musaf is 

ה ו י ה

It comes from the pasuk in Devarim 

ט) וַיְדַבֵּ֤ר מֹשֶׁה֙ וְהַכֹּהֲנִ֣ים הַלְוִיִּ֔ם אֶ֥ל כׇּל־יִשְׂרָאֵ֖ל לֵאמֹ֑ר הַסְכֵּ֤ת ׀ וּשְׁמַע֙ יִשְׂרָאֵ֔ל הַיּ֤וֹם הַזֶּה֙ נִהְיֵ֣יתָֽ לְעָ֔ם לַיהֹוָ֖ה אֱלֹהֶֽיךָ׃ 

(9) Moses spoke, and the levitical priests, to all Israel, saying: Hasket! Hear, O Israel! This very day you have become the people of your God יה - - וה:

Rav Yisrael Simcha Schorr quotes an Agra d’Kallah (from the Bnei Yissaschar) that cites a Zohar at the end of Parshas Pinchas which states that Yaakov and Esav divided the months between themselves. Yaakov symbolizes the middas harachamim, compassion, while Esav symbolizes the middas hadin, justice. Certain months are connected more to din and others are connected to rachamim. Esav wanted to take all the summer months, Tammuz, Av, and Elul. As we know, Tammuz and Av are difficult months for us, times of din. However, Yaakov would not allow Esav to take the month of Elul, as it would be too hard on Klal Yisrael to come into the din of Rosh Hashanah without the rachamim of Elul. We need Hashem’s compassion for a full month in order to face the great Day of Judgment.

Esav complained that Yaakov has tricked him twice, that he had taken away from him those two months.

Every year during the month of Elul, this struggle between Yaakov and Esav is renewed. Esav wishes to retrieve the month for himself. 

Yaakov in seeking ways to sweeten jusgment with lovingkindness, Ya’akov managed to liberate the second portion of Av from Esav. (This took place when he defeated the Sar of Esav in the 'wrestling' match. The result is that now the second half of Av is joined with the entire month of Elul, the month of Teshuvah, the best time for getting back into alignment with the Divine will. Indeed, the Holy Qedushat Levi, Rebbe Levi Yitzhak of Berditchev, noted that Av is an acronym for Arur (cursed) and Barukh (blessed). The blessing part of Av begins with this parashah and reaches its height on the 15th of Av.