I've always heard about the mother of the devas or precisely Indra that is Aditi. But who according to Hinduism is the father of Indra?
Indra's father is the sage Kashyapa, son of the sage Marichi who is one of the mind-born sons of Brahma. Kashyapa married numerous daughters of Brahma's other son Daksha, including Aditi, mother of the twelve Adityas which include Indra. This is confirmed in numerous scriptures. Here is what the Aranya Kanda of the Ramayana says, for instance:
Of them Kashyapa accepted eight slender-waisted daughters of Daksha Prajapati, namely Aditi, Diti, Danu, Kaalakaa and Taamra, Krodhavasha, also thus Manu and even Anala also as wives. Then Kashyapa is gladdened and said to those young wives, "You all shall deliver sons similar to me and who can sustain the three worlds." ... Aditi gave birth to twelve Adityas, the Sun-gods, eight Vasu-s, the Terrestrials-gods, eleven Rudraas, the Fury-gods, and two Ashvinis, the medicine-gods, total thirty-three of them.
And here is what the Adi Parva of the Mahabharata says:
And [Dakaha] bestowed ten of his daughters on Dharma, and thirteen on Kasyapa. And he gave twenty-seven to Chandra, who are all engaged in indicating time. And Kasyapa, the son of Marichi, begat on the eldest of his thirteen wives, the Adityas, the celestials endued with great energy and having Indra as their head and also Vivaswat (the Sun).
Finally, here is what the Srimad Bhagavatam says:
[Daksha] gave ten daughters in charity to Dharmarāja [Yamarāja], thirteen to Kaśyapa [first twelve and then one more], twenty-seven to the moon-god, and two each to Aṅgirā, Kṛśāśva and Bhūta. The other four daughters were given to Kaśyapa.... O King Parīkṣit, now please hear from me the names of Kaśyapa’s wives, from whose wombs the population of the entire universe has come. They are the mothers of almost all the population of the entire universe, and their names are very auspicious to hear. They are Aditi, Diti, Danu, Kāṣṭhā, Ariṣṭā, Surasā, Ilā, Muni, Krodhavaśā, Tāmrā, Surabhi, Saramā and Timi.... Now please hear me as I describe the descendants of Aditi in chronological order. In this dynasty the Supreme Personality of Godhead Nārāyaṇa descended by His plenary expansion. The names of the sons of Aditi are as follows: Vivasvān, Aryamā, Pūṣā, Tvaṣṭā, Savitā, Bhaga, Dhātā, Vidhātā, Varuṇa, Mitra, Śatru and Urukrama.
Shatru is another name for Indra.
The Puranas make Aditi and Kashyap Indra's father but according to Rig Ved Verse 1.164.33 Indra is born of Dyaus and Prithvi - the Sky Father & Earth Mother:
31 I saw the Herdsman, him who never stumbles, approaching by his pathways and departing. He, clothed with gathered and diffusive splendour, within the worlds continually travels.
32 He who hath made him cloth not comprehend him: from him who saw him surely is he hidden. He, yet enveloped in his Mother's bosom, source of much life, hath sunk into destruction.
33 Dyaus is my Father, my begetter: kinship is here. This great earth is my kin and Mother. Between the wide-spread world-halves is the birth-place: the Father laid the Daughter's germ within it.
Again RV Verse 4.17.4 mentions:
3 Hurling his bolt with might he cleft the mountain, while, putting forth his strength, he showed his vigour. He slaughtered Vṛtra with his bolt, exulting, and, their lord slain, forth flowed the waters swiftly.
4 Thy Father Dyaus esteemed himself a hero: most noble was the work of Indra's Maker, His who begat the strong bolt's Lord who roareth, immovable like earth from her foundation.
Verse 1.191.6 also mentions the same:
6 Heaven is your Sire, your Mother Earth, Soma your Brother, Aditi Your Sister: seeing all, unseen, keep still and dwell ye happily.
I personally favor the Puranic version since it is most complete. However, Dyaus and Indra do resemble in many ways both being the rulers of Heaven so the association seems plausible.