I believe Carl Friedrich Gauss is a close second to Euler.

Someone · on April 30, 2020

For those who want to compare them:

- https://en.wikipedia.org/wiki/List_of_things_named_after_Leo...

- https://en.wikipedia.org/wiki/List_of_things_named_after_Car...

Judged by the number of multiple-surname ‘things’ on both pages, Gauss seems to have been more of a collaborator, or more of his discoveries were also made by others at about the same time.