In a galaxy where everything wants to kill you, and one person's psychic power is holding the empire all together, they name this ship after that guy.
About this creation
"The Emperor-class Battleship is a slow and ponderous vessel that serves as one of the mainstay capital ships of the Imperial Navy."
Taken from the Warhammer 40K Wikia, the above quote serves to highlight the enormity of the ship. Broadside lance heavy, with 8 Attack Squadrons for longer range engagements, and typically a large number of escort frigates for dealing with faster targets, this capital ship is a favourite for leading an fleet engagement.