Gill Sans and Zapf's Optima were the first big humanist fonts, but they are really best used sparsely. Zapf died earlier this year, by the way.
But with Adrian Frutiger's Frutiger the whole world was blown open. Helvetica had a predecessor fairly like it in Akzidenz Grotesk, but Frutiger was something else entirely. Grotesques had been around for decades prior to Helvetica. Frutiger was a revolution. I and everybody should know that our visual world is markedly different because of Adrian Frutiger.
Right now, I am on a Windows tablet. Segoe UI, Tahoma, Arial, Verdana, Calibri, Microsoft's (and Matthew Carter's in particular) font efforts here were, but for Arial, so very much direct descendants, if not copies, of Frutiger's Frutiger. The default font in Microsoft Word must count Frutiger as it's most influential ancestor, bar none.
On Mac OS X, Lucida Sans is just the same, carrying Frutiger's DNA utterly. And on Linux, Bitstream Vera is just the same.
And it's not just Frutiger. Mac OS X's new default font, San Francisco is very much Univers, with some DIN. Univers is the designer's default font of choice for anywhere that Helvetica isn't chosen. I love its condensed form, as used here by Australia Post, and its numbering system was influential too and expressed an incredible range of variation within a single family. It is the ultimate tight font.
Avenir was a wonderful reinterpretation of Futura, Serifa is the most sensible slab serif, and the only generally acceptable one next to Rockwell... and that's nothing to say of the cross-pollination of his Frutiger with Univers and Helvetica. Think Roboto and basically half of what's on Google Fonts.
His influence on Erik Spiekermann, who drew some fonts that blew the visual landscape open in the 90s and early 2000s is insane when combined with the dutch Thesis and Scala. His influence on every fixed width font that has become popular on computers after Courier New is similarly huge.
Adrian Frutiger is, with no doubt, the person that drew our languages the most in the past century, Akzidenz Grotesk coming from 1896. His shapes influenced every comment you read here more than any other person in the past century. He made things legible and beautiful. Even for computers he did, with OCR-B.
I think that now with us in a post-Frutiger era, it's going to take a very, very long while for someone to come along and change our written language and visual world with such a bombshell as he did. If ever again - that is a very serious question.
We are now entering an area where there's fewer new ideas, but refinement and cross-pollination. The landscape seems like it's settling, with typefaces like Gotham and San Francisco and Roboto being very evolutionary... but with not that much of a way forward? There's been few new strands of DNA in the typeface world since Spiekermann's Meta. (and its very contemporary siblings Thesis and Scala)
Let's hope that like the Dalai Lama, we can find Frutiger reincarnated in a new form so that in a few decades he may once again shine us a light and bring to us a genuine future, like his Frutiger had brought upon us before.
Either that or we just A-B test signage typefaces out the wazoo and see if something as amazing as that somehow emerges a million generations from now, possibly even within the confines of the Latin alphabet. DIN 1451, which had some influence an Frutiger, isn't spent yet, I don't think. Meta probably is spent by now. Gill Sans is getting close, because of Gotham. Frutiger is getting there :/
We now live in a post-Frutiger world. That's kind of scary, if you think about it.
Whatever comes, I hope to at least see the next Frutiger's work and what it means for mankind before I die. I expect it to be interesting.