Ah, right, yes. Not a stupid question at all - having been completely immersed in this forever I sometimes sort of forget that not everyone is! And I tend to use first-person pronouns for both Debian and Ubuntu depending on which hat I'm wearing for a given sentence, which probably doesn't help much.
I've been helping to develop Debian since 2000 or so, and the initial pool of Ubuntu developers mostly came from the Debian community (also GNOME and one or two other places). Part of the legend, which in this case I think is mostly true, is that Mark went on an icebreaker trip to Antarctica in late 2003 and took a copy of the debian-devel mailing list archives with him for light bedtime reading so that he could get an idea of whom to hire. I always did free software work because it seemed like a useful and ethical thing to do with my skillset rather than because it might get me hired, but in this case it turned out to help both ways.
Anyway, Debian is technically called a distribution, in that it takes source code from upstream developers (the standard metaphor is that of a river of code flowing downstream), packages it so that people can get at it in a unified standard way without having to figure out how to cope with all the different ways developers release their software, and distributes it from a central place. Ubuntu is also a distribution, but is technically a Debian derivative: it takes large parts of its source code from Debian (which of course distributes its source code and build scripts and such), builds it independently, and assembles it differently.
Since it's free software the licences in general allow for modification and redistribution. To start with, Ubuntu made a fairly minimal set of changes on top, basically things like making the installation process flow the way we wanted, adjusting the default desktop to the way we wanted it to look, and fixing some bugs in advance of the relevant Debian maintainer getting round to it. As time has gone on our set of changes has got a good deal larger, and in some cases we now either bypass Debian and take code directly from upstream or else do our own upstream development; for instance the Unity desktop environment is developed by Canonical and not packaged in Debian. However, the bulk of the packages available in the Ubuntu archive still come basically unmodified from Debian, even though most of the stuff that's front-and-centre is bespoke or modified in some way. A lot of this is for economic reasons, because it would be really expensive in both time and money to replicate the huge archive of 20000+ source packages that Debian has already put together (a lot of which is niche in some way, of course, but it's often very useful to have that breadth available), and it wouldn't actually make things any better for users if we tried. We do spend a considerable amount of effort just keeping up - any time we make changes to a package, we have to merge those forward to newer versions until such time as they're integrated further upstream from us, if ever - but a lot of that is at least semi-automatable and it's still a lot easier than doing it all from scratch.
In terms of the community, it's been complicated. On the one hand, Canonical employs a bunch of people to do free software development, and a lot of that ends up flowing back to Debian; we send a lot of patches back in bug reports, and there are quite a few packages we just maintain in Debian directly for various reasons (maybe we have the best person for the job, maybe it's just simpler that way, or whatever). That sort of thing is generally supposed to be good. On the other hand, a lot of people resented us creating our own distribution rather than putting the same effort purely into making Debian better, we often get accused of not contributing enough back (sometimes fairly, sometimes not), and some people just don't like the kinds of changes we make. There are plenty of developers who consider themselves part of both communities, myself included. By this point things have stabilised - Ubuntu is obviously around for the long term, some people in Debian are pretty much resolved to dislike whatever we do, but a lot of others are happy to work with us so we can spend a reasonable chunk of time actually getting stuff done rather than arguing about it.
Debian and Ubuntu are two major examples, but if you don't try to be quite so general-purpose then setting up a Linux distribution doesn't require hundreds of people, especially if you base your work on something that already exists, and it's often a useful way to try out different approaches at a medium scale. As a result the distribution world is fearsomely complicated and entangled; there's an amazing chart on Wikipedia (https://upload.wikimedia.org/wikipedia/commons/1/1b/Linux_Distribution_Timeline.svg) which tries to visualise everything anyone's ever done in this space and how they relate to each other, and I've only even heard of a ridiculously small fraction of them.
no subject
I've been helping to develop Debian since 2000 or so, and the initial pool of Ubuntu developers mostly came from the Debian community (also GNOME and one or two other places). Part of the legend, which in this case I think is mostly true, is that Mark went on an icebreaker trip to Antarctica in late 2003 and took a copy of the debian-devel mailing list archives with him for light bedtime reading so that he could get an idea of whom to hire. I always did free software work because it seemed like a useful and ethical thing to do with my skillset rather than because it might get me hired, but in this case it turned out to help both ways.
Anyway, Debian is technically called a distribution, in that it takes source code from upstream developers (the standard metaphor is that of a river of code flowing downstream), packages it so that people can get at it in a unified standard way without having to figure out how to cope with all the different ways developers release their software, and distributes it from a central place. Ubuntu is also a distribution, but is technically a Debian derivative: it takes large parts of its source code from Debian (which of course distributes its source code and build scripts and such), builds it independently, and assembles it differently.
Since it's free software the licences in general allow for modification and redistribution. To start with, Ubuntu made a fairly minimal set of changes on top, basically things like making the installation process flow the way we wanted, adjusting the default desktop to the way we wanted it to look, and fixing some bugs in advance of the relevant Debian maintainer getting round to it. As time has gone on our set of changes has got a good deal larger, and in some cases we now either bypass Debian and take code directly from upstream or else do our own upstream development; for instance the Unity desktop environment is developed by Canonical and not packaged in Debian. However, the bulk of the packages available in the Ubuntu archive still come basically unmodified from Debian, even though most of the stuff that's front-and-centre is bespoke or modified in some way. A lot of this is for economic reasons, because it would be really expensive in both time and money to replicate the huge archive of 20000+ source packages that Debian has already put together (a lot of which is niche in some way, of course, but it's often very useful to have that breadth available), and it wouldn't actually make things any better for users if we tried. We do spend a considerable amount of effort just keeping up - any time we make changes to a package, we have to merge those forward to newer versions until such time as they're integrated further upstream from us, if ever - but a lot of that is at least semi-automatable and it's still a lot easier than doing it all from scratch.
In terms of the community, it's been complicated. On the one hand, Canonical employs a bunch of people to do free software development, and a lot of that ends up flowing back to Debian; we send a lot of patches back in bug reports, and there are quite a few packages we just maintain in Debian directly for various reasons (maybe we have the best person for the job, maybe it's just simpler that way, or whatever). That sort of thing is generally supposed to be good. On the other hand, a lot of people resented us creating our own distribution rather than putting the same effort purely into making Debian better, we often get accused of not contributing enough back (sometimes fairly, sometimes not), and some people just don't like the kinds of changes we make. There are plenty of developers who consider themselves part of both communities, myself included. By this point things have stabilised - Ubuntu is obviously around for the long term, some people in Debian are pretty much resolved to dislike whatever we do, but a lot of others are happy to work with us so we can spend a reasonable chunk of time actually getting stuff done rather than arguing about it.
Debian and Ubuntu are two major examples, but if you don't try to be quite so general-purpose then setting up a Linux distribution doesn't require hundreds of people, especially if you base your work on something that already exists, and it's often a useful way to try out different approaches at a medium scale. As a result the distribution world is fearsomely complicated and entangled; there's an amazing chart on Wikipedia (https://upload.wikimedia.org/wikipedia/commons/1/1b/Linux_Distribution_Timeline.svg) which tries to visualise everything anyone's ever done in this space and how they relate to each other, and I've only even heard of a ridiculously small fraction of them.