What's a Good Set of Roles to Have Within a Team?

Questions by Mhairi Mcclair in September 2018

What make a good technical team? Think of the best team you worked on…what made it a good team?
What attributes do you want people to have on such teams?
What types of roles do you find on technical teams?
What would be a good mixture of roles?
What is the job of the team leader?
What responsibilities do developers have?
Who is responsible for quality?
Should testers and designers be part of the development team, or separate departments for each?
Should you have separate front end and back end developers? Or full stack?
How does Devops fit in?
How can you check whether your team structure is working?