The functional roles of herbivores and carnivores in ecosystems are relatively well studied, they exert top-down direct and indirect control and can modify ecosystems through engineering. Omnivores lie at the interface between these two guilds, and because they may consume a little of everything, their role in ecosystems has been somewhat overlooked. However, for these reasons we believe that omnivores play a pivotal role in ecosystems through trophic and non-trophic interactions with other guilds, from primary producers to apex consumers. To gain a better understanding, we performed a literature review for both interactions triggered by a group of terrestrial omnivores: Bears. We submitted equation searches on the Web of Science for each type of interaction and omnivore bear species. We kept 411 references highlighting a wide range of trophic and non-trophic interactions in various ecosystems. Our review shows the large number, diversity and significance of interactions in the ecosystem due to omnivorous bears, but also a huge global variability in interactions from bear to bear species and among sites. We argue, even if further research is required, that omnivores may constitute keystone species, not solely due to few strong interactions but rather to multiple interactions of varying strength with various ecosystem components, turning them into potential targets for ecosystem conservation.