One of the requirements for his role was " put on weight "
https://www.theguardian.com/tv-and-radio/2021/aug/28/north-water-bbc-amc-colin-farrell-stephen-graham-jack-oconnell-andrew-haigh
" Drax’s sheer presence on the page demanded a startling physical transformation from Farrell. “Colin reminds me of Bluto from Popeye,” Graham observes accurately. “A colossus, a monster of a man.” Farrell, all brawn and heft, explains: “I ate a lot and lifted some heavy weights. I looked at Victorian boxers and dockers, trying to get the belly and the muscle. It was not done under the supervision of medical professionals at all and was really ill advised.”