A Guru in Hinduism is of paramount importance in spiritual matters. So I want to know who were the gurus of Guru Brihaspati and Sukracharya? I heard that Shiva taught Shukra the art of reviving the dead. But I haven't come across any teacher for Brihaspati. Also, I don't think Shukra had only one teacher. Are there any names mentioned in the Puranas?
The Devi Bhagavata Purana (Book 9; Chapter 4) talks about a particular Saraswati Mantra.
During different times the Mantra is said to have been imparted by various Gurus to their respective disciples.
Besides all should worship the Devî Sarasvatî on the day of commencement of education and every year on the S’ûkla Panchamî day of the month of Mâgh. The eight-lettered Mantra, as mentioned in the Vedas is the root Mantra of Sarasvatî. (Aim Klîm Sarasvatyai namah). Or the Mantra to which each worshipper is initiated is his Mûlmantra (not Mantra).
Or uttering the Mantra “S’rîm Hrîm Sarasvatyai Svâhâ” one is to offer everything to the Devî Sarasvatî.
This Mantra is the Kalpa Vriksa (i. e., the tree which yields all desires). Nârâyana, the ocean of mercy, gave in ancient times, this very Mantra to Vâlmikî in the holy land Bhârata Varsa on the banks of the Ganges; next Bhrîgu gave this Mantra on the occasion of solar eclipse to Maharsi Sukrâcharya on the Puskara Tîrtha; Mârîcha gave to Brihaspati on a lunar eclipse; Brahmâ gave to Bhrîgu in the Vadarikâ Âs'rama; Jaratkarâ gave to Âstika on the shore of the Ksiroda ocean; Bibhândaka gave this to the intelligent Risyasringa on the Sumeru mountain, S'iva gave this to Kanâda and Gotama, Sûrya gave to Yâjñavalkya and Kâtyâyana, Ananta Deva gave to Pânini, to the intelligent Bhâradvâja and to S'âkatâyana in Bali's assembly in the Pâtâla. If this Mantra be repeated four lakhs of times, all men attain success. And when they become Siddhas with this Mantra, they become powerful like Brihaspati. In past times, the Creator Brahmâ gave a Kavacha named Vis'vajaya to Bhrîgu on the Gandhamâdana Mountain. I now speak of that.
So, for those particular initiations, Maricha and Bhrigu were the Gurus of Brihaspati and Shukra respectively. And, there can be many more such Gurus for both of them.
(BTW I'm not sure who is Maricha here. Is Marichi mistyped as Maricha? One Maricha was of course a demon from Ramayana)