Vivekachudamani 1

सर्ववेदान्तसिद्धान्तगोचरं तमगोचरम् । गोविन्दं परमानन्दं सद्गुरुं प्रणतोऽस्म्यहम् ॥ १ ॥ sarvavedāntasiddhāntagocaraṃ tamagocaram | 
govindaṃ paramānandaṃ sadguruṃ praṇato'smyaham || 
(Vivekachudamani 1) 

My salutations to Sri Sad-Guru Govinda who is of the nature of Bliss Supreme, who can be known only through the import of the essence of Vedanta and who is beyond the reach of the known instruments of perception. 

 Adi Shankara, the propagator of the Advaita philosophy, non-dualism, meeting his Guru, Govinda Bhagavatpāda. The Guru is many things, including being a teacher of skills, a counselor, one who helps in the birth of mind and realization of one's soul, who instills values and experiential knowledge, an exemplar, inspiration and who helps guide a student's spiritual journey.