Paul Erdős was an extraordinary mathematical collaborator. He traveled constantly, cross-pollinating the mathematical community. He wrote about 1500 papers and had around 500 coauthors. According to Ron Graham,
He’s still writing papers, actually. He’s slowed down. Because many people started a paper with Erdős and have let it lay in a stack some place and didn’t quite get around to it … In the last couple years he’s published three or four papers. Of course he’s been dead almost 15 years, so he’s slowed a bit.
For more on Erdős, listen to Samuel Hansen’s excellent podcast.