Altavista was initially a demo of the capabilities of DEC Alpha CPUs. It was initially amazing. It got taken over by SEO rubbish, and beaten by Google who invented PageRank to get good results again.

PageRank was initially much less prone to SEO shenanigans because it relied on signals from other sites (incoming links) to decide how important a result was. Of course, as Google became more popular, people started sharing links on other pages and so on to cheat the PageRank algorithm. And Google have been caught in a fight with SEO ever since.