The teaching mentioned in Mundaka Upanishad are first told by Lord Brahma to Atharvan (अथर्वा ), than Atharvan told rishi Angir (अङ्गिरः) , Angir told to Satyavaha (सत्यवह ) who was born in Bharadwaj gotra, the Satyavaha than passed this teaching to his student and son to Angiras (अङ्गिरसः) , both the higher and the lower knowledge.
This hierarchy is mentioned in starting verses of the Mundakopanisad itself.
अथर्वणे यां प्रवदेत ब्रह्माथर्वा तं पुरोवाचाङ्गिरे ब्रह्मविद्याम्।
स भारद्वाजाय सत्यवाहाय प्राह भारद्वाजोऽङ्गिरसे परावराम् ॥ – mundakopanisad 1.2
शौनको ह वै महाशालोऽङ्गिरसं विधिवदुपसन्नः पप्रच्छ। – mundakopanisad 1.3
कस्मिन् नु भगवो विज्ञाते सर्वमिदं विज्ञातं भवतीति ॥
Shaunaka (शौनक), the great householder and the son of Rishi Sunaka (शुनक), came to Angiras (अङ्गिरसः) in the due way of the disciple and asked of him, “Lord, by knowing what does all this that is become known?”
The whole Upanishad is the teaching passed on the rishi Angiras (अङ्गिरसः) to rishi Shaunaka (शौनक).