Klingon verbs don't mark tense, so it could be past, present or future. Most of the time, you can tell tense from context or time adverbs. But these beginning sentences are trying to keep it simple, so no context or adverbs. Thus, you can put any of the three tenses.
In this case, Kahless (not counting his clone) died before the timeframe of the Star Trek shows started, so it would make sense to make this sentence past tense.