I am looking for any and all materials about Antii Isotalo. He's a bit infamous in my family, as I have been told he is an ancestor. All I really know is from…

There are actually three famous Finns by the name of Antti Isotalo: the farmer and knife-fighter Antti Heikinpoika Isotalo or Isoo-Antti (1831 - 1911), his grandson Antti Isotalo (1895 - 1964), and the unrelated preacher Antti Matinpoika Isotalo (1824 - 1906). Since the first two have English Wikipedia pages, I assume you mean either of them.

Unfortunately, there is not much information available in English about these men, apart from the Wikipedia pages. The blog Your Roots uses Antti Heikinpoika Isotalo as an example in demonstrating how to use Finnish genealogy records, so there is some information about him in this and this blog entry, as well as some of the subsequent ones.

Finnish online resources include the National Biography of Finland, which has articles on both Isoo-Antti and his grandson. Below are some more Finnish articles and books which contain some information about Isoo-Antti:  

"Häjyt - Antti Isotalo - Härmän häjy"

"Häjyt – Pohjanmaan sitkein myytti"

Pohjanmaan Väylän matkailuhakemisto. Henkilöhistoria: Isotalo Antti

Ylikangas, Heikki. Härmän häjyt ja Kauhavan herra : kuvaus puukkojunkkareitten ja virkavallan välisestä yhteenotosta 1860-luvun lopulla (Otava 2005).

Aalto, Ensio et al. Rannanjärvi on kuallu ja Isontaloon Antin tarina (Jussituotteet Art Tifani 2013) (A fictionalised comic book version of the story).

Härmän häjyt (A documentary about the knife-fighters and their role in Finnish culture, no subtitles).

"Isontalon Antti ja Rannanjärvi" (A video of the famous traditional song, with English subtitles).

The grandson's life is chronicled in detail in the books Isontalon Antti: eteläpohjalainen jääkäri, värväri ja seitsemän sodan veteraani (Suomalaisen kirjallisuuden seura 2007) and Suomalaisia soturikohtaloita (Suomalaisuuden liitto 1998), both by Jussi Niinistö.