Originally planned as the Githduros1, the Dakeen were created by Matt Colvile for Liber Bestarius.
Githduros were mentioned during a Matt Colville Stream3:
Hey- hey, are you a Gith? … It’s been a looong time since a Gith has come in here. Hey which kind of Gith are you? He’s like 'Oh I bet I could guess cuz there’s a couple right? There’s like th-uhhh- there’s the Githzerai … and one goes yeah and there’s the Githduros, and he goes no I think that one’s a Githyanki
While Colville is associated with Critical Role, and Critical Role is canonical to D&D, this stream was in an unrelated campaign, and so is not likely canon.
The Dakeen were primarilly scouts, serving the aeon. Upon freeing themselves from extraplanar control, they became planar rangers, renowned for their skills across the multiverse2.