The founder, Dmytro Gerasymenko, set up his first simple online database of links when he was still at school, but he lost all of that due to a server crash. He didn't back up.
He started it all over again after a few years. Site Audit was Ahrefs' only tool at its launch. It was supposed to be just an indexing system and a web crawler.
Ahrefs' team didn't do much marketing. They just posted some ads on forums for SEO specialists and marketers. They got their first users. Those people brought others through word of mouth because the guys had a really cool product of high quality.
Other than the forum ads, in the beginning, Ahrefs had no other adverts or any direct marketing strategies. They focused on their product instead.
They hired Tim Soulo. He became their Head of Marketing. At first, Ahrefs was just a good backlink analytics tool (they stormed that niche), but that wasn't enough. Tim was a great writer. He reworked Ahrefs' UI and focused on their blog. People started telling him the blog made them want to try Ahrefs.
He went hard on the blog explaining how to use Ahrefs to make their SEO work efficiently. He knew what people searched for. He also ran some low-cost Facebook ads.
[source]