Kay Sievers wrote udev, which Lennart swallowed into systemd and proceeded to make unusable outside his own pet configurations. Exclude the pre-existing udev, which was and should have remained a separate project, and it's all Lennart.
Also udev merge into systemd would have not happened without Kay's consent.
And I don't understand why people get downvoted just beacuse they correct you.
[Edit] Typos
udev and systemd are two separate projects who happen to live in the same repository (nothing wrong with that!) so you have to remember to exclude udev when looking at contributors for systemd.
The git can not show that. And unless Kay himself state the contrary we will not know. Lennart says Kay was associated to the project from the start. If it were not true, wouldn't have Kay said something by now ?
I don't always agree with directions Lennart goes, or on the methods. But that does not justify ferocious ad hominem attacks I've read.
edit: @nknight followup:
Did you even look into git for yourself? Even with excluding udev the top contributors are:
On what planet is that "all by Lennart"?!