Consider the colon in bold, which is used to connect two sentences. If it is not the best choice, replace it with a different punctuation mark. Though Franz Kafka later became well known as a fiction writer, during his lifetime he supported himself with a less glamorous occupation: he processed and investigated claims for a large insurance company.

The colon in the sentence is used correctly to introduce an explanation or elaboration of the preceding clause. Therefore, it does not need to be replaced. The sentence is punctuated correctly as follows:<br /><br />"Though Franz Kafka later became well known as a fiction writer, during his lifetime he supported himself with a less glamorous occupation: he processed and investigated claims for a large insurance company."<br /><br />If you still want to consider an alternative punctuation mark, a semicolon could also work, but it would slightly change the emphasis:<br /><br />"Though Franz Kafka later became well known as a fiction writer, during his lifetime he supported himself with a less glamorous occupation; he processed and investigated claims for a large insurance company."<br /><br />However, the original colon is the best choice here because it clearly introduces the specific nature of Kafka's occupation.