Lennart Poettering is the by far most controversial and famous software developer in the free software community. He works for IBMs subsidiary Red Hat. He created and maintains several rather heatedly debated pieces of software such as systemd, pulseaudio and avahi.
All the drama
There's been a whole lot of upset people posting negative remarks against Poettering. Much of the hate against Poettering is simply based on differing opinions. There are, however, a lot of valid criticism based on very valid technical arguments. Poettering is openly against the Unix philosophy of making small programs that do one thing well. He as also openly argued against POSIX. Further, he's claimed that BSD, which arguably has much better security than any of his software will ever have, "is not relevant anymore". In the above 2018 video he explains how the vast majority of machines run Linux whereas BSD, Solaris, UNIX and such have only a tiny installed base. This was different in 1975 but this is the 21st century.
Poettering got a lot of hate for creating and pushing PulseAudio the first half-dozen years of it's existence. Some of it was unfounded, some was not. PulseAudio didn't actually work right with SPDIF, specially when trying use pass-through, until SPDIF was obsolete. PulseAudio was released in 2004 and it wasn't really usable until 2014. It has become a standard part of the Linux audio stack and the modern version is fine.
The CCC incident
Lennart Poettering did in fact walk up on stage with a beer in hand while someone was doing a presentation which criticized some of the software written by Poettering at a Chaos Communication Congress years ago. While there is no defense for this behavior it is something that happened long ago when Poettering was young. He's probably (hopefully) grown up since then.
The dream of a a Poettering-Free Linux
Let's say you want to reboot directly into your machines EFI BIOS. How do you do that?
systemctl --firmware-setup reboot
That's one of the things we now take for granted thanks to the very controversial init manager systemd - created by Lennart Poettering.
And how do you easily see exactly how much time the various boot services spend starting up?
That's - again - "Poettering software".
We could go on but you get the idea: For all the controversy and criticism the fact is that there are real advantages to most of the software Poettering's written. A lot of simple features would simply not be there on a distribution totally void of any software he's touched.