ROS guru: Understands the nitty gritty details of ROS (e.g. what's the difference between a topic and a message?) and knows how to use different ROS tools.
Perception guru: Understands sensor data and can write software for processing it.
Hardware guru: Understand the hardware, is not afraid of using a screw-driver or a 3D printer.
Design and fabrication guru: Makes sketches of ideas, knows 2D and 3D computer-aided design tools, knows how to operate the laser cutter and 3D printer.
User interface guru: Understands human factors and usability, makes things look good.
Manager: Makes sure every team member is on the same page at all times. Help make decisions (layout pros and cons). Enforce "interface agreements" so components can be easily integrated.
Documentation and communications: Makes videos, takes notes, writes blog posts, gives presentations.