There's little question that some parts of "The Elements" were added by later authors. Heath's English translation gives a lengthy commentary on what is likely in the original work and what is known or suspected to be from later editors.
There were also two entire books tacked onto the end that were often attributed to Euclid, but are now generally recognized as being from later authors.
So in that sense the author of the Elements wasn't just one person. But there almost certainly was an actual Euclid who wrote the bulk of what's come down to us as The Elements. Pappus and Proclus both discuss him as an actual person, and while they lived several centuries after The Elements were written, we know they were drawing from near-contemporary sources.