"Kal'ger the Warmonger" is a unique and specific phrase that may not have many synonyms that directly replace it. However, one could use words that evoke a similar meaning or feeling such as "militant leader", "aggressive conqueror", or "belligerent commander". Other options could focus on the warmongering aspect and use "battle-driven ruler", "war-hungry strategist", or "hostility-loving general". Each synonym brings its own nuance or emphasis to the original phrase, but all convey a sense of someone who is willing to use military force to achieve their goals.
