Lanius was a former Scolemis general and the head of the Kanto arm of the Pokepan invasion during the events of the AU Arc. A brutal though intelligent combatant three times the size of an average Samurott, he was a fan of the Roman practices of crucifixion and decimation and headed an army of slavers and murderers. Many of these mons were likely only in what counted as late adolescence amongst their species.
Lanius was also a Social Darwinist with a firm belief that the strong had a right to rule over and cull the weak, as he stated before he fought members of the J-Team in Celadon. Lanius's Social Darwinism was joined by his very chauvinistic views towards females, disallowing them to fight among his forces and seeing them as little more than slaves and/or breeding stock. After Tagg, Tracer, Every, Mezzo, and Fool and their mons defeated him in an epic battle, (With some help from Ian and his friends.) Tracer paralyzed him below the neck using Tagg's own dagger to make him even lower than those he considered lesser. Eventually he ended up putting his energy into bloody war poetry, and in the PMD-B timeline ended up creating an entire settlement of larger than normal marine mammal mons within PEFE HQ.
Lanius's NPC handler is Tagg.
In the OU
Within the OU, Lanius is simply the leader of an Oshawott rookery. While still kind of a jerk, he's nowhere near as bad as his AU counterpart.
Being not only large, but incredibly resilient to all kinds of damage to match, Lanius was a particularly fearsome opponent. He was able to remain standing after massive salvos fired by Tagg's mons, and managed to put Musashi, Gaia, Vanilluxe, Lake, and Nadia in the ICU. Besides being able to hit someone so hard with his seamitars or paw that they'd be temporarily rendered unable to move, and being incredibly fast and deadly at close range, Lanius had the unique ability to freeze his seamitars in order to better kill Dragon type Pokemon, which he used to heavily injure Nadia.