Some species are more mellow, but the most common, the banded leporinus, is a fin nipper (at the least aggressive). They are also incredibly territorial and have them same dominance complex as cichlids. Mine would go head to head against a piranha (and lived to tell about it), he now is with cichlids and is the dominant fish. They also don’t seem to like anything in their size range as they grow (and will shred the fish they don’t like).
Previous ones I had would stake out a territory and kill fish that came close and wouldn’t leave.