What is the name of the robot enemy in "Sonic and Knuckles"?

[SoniX 2]

If you choose to play as Knuckles you get this robot guy flying this machine, instead of eggman

0:20 - 0:38

 

3:02 - 3:31

[Skye Prower 386]

Eggrobo

 

Actually a minor minion boss of Robotnik.  You fight a lot of them as Sonic in the Sky Sanctuary level.  Here it's being used to hide the fact Mecha-Sonic is the mastermind in the Knuckles story.

[Blue Comet 11]

Eggrobo 

 

You fight them in Sonic's Sky Sanctuary zone and was a minor boss you fight as Knuckles into you found out it was Mecha Sonic behind everything. He's also unlockable in Sonic R and Sonic Adventure 2 Kart race as an alternate skin for Dr. Eggman.