肩吾 Jiānwú appears to be a fictional character who appears nowhere outside of Zhuangzi. 肩 jiān means "shoulder" or "to shoulder" and 吾 wú is a first-person pronoun. To take oneself on one's should sounds as paradoxical as lifting oneself up by the bootstraps, hence my translation.
He appears in 1:05, where he tells Step-Brother about his conversation with Jie Yu; 6:03, where he is listed as the spirit of Mt. Tai (though this is attested nowhere else); and in 7:02 where has a conversation with Jie Yu (though it sounds like a different one from the one referred in 1:05).