Calot is the leader of the pirates that took over Kett spaceship. The fight with him is a part of the side quest called Liam Kosta: All In which is Liam's loyalty mission. The confrontation with Calot is during the final part of said quest.
In default Calot is located behind a powerful shield that can be pierced by normal attacks. You must perform actions that will disable the force field.
In order to destroy Calot's shield you must hack two access points. The first one is on the left from the starting point. When you reach it you must stay close to it so the hacking process can be completed. Sadly, this is related to one serious hindrance because nearby a captive Eiroch will appear. Do not allow this monster to get close to your character. USe shotguns, grenades, mines and skills that weaken enemies from a short or medium distance.
Shortly after that, the hacking process is interrupted and you must reach the second access point. It is located on the upper level, right from the starting point. It works in the same way as the first one so, after starting the hacking, you must defend yourself. In this case you must "only" fight with pirates and Adhi beasts. The enemies can come from two different directions so you should place your team mates on the left and right from the access point.
Defend yourself until the hacking bar is completely full. The force field, behind which Calot was hiding, is now disabled. You don't have to rush in order to get to him because he won't regain the shield. First, deal with all pirates that stand between you and Calot. After their death you can get rid of their leader in any way that you want - fortunately, he is an easy enemy to defeat.