Final answer:
King Ezana of the Kingdom of Aksum was the Christian king who subdued the Beta Israel and established one of the earliest Christian states by replacing traditional symbols with the Christian cross.
Step-by-step explanation:
The Christian king who finally subdued the Beta Israel was King Ezana of the Kingdom of Aksum. Between 330-340 CE, King Ezana embraced Christianity, marking a significant religious transformation for Aksum, which had previously been a polytheist state. Through military campaigns, notably against the Kingdom of Kush, King Ezana expanded his kingdom and promoted Christianity.
Coinage from his reign displays the replacement of earlier symbols with the Christian cross, signifying the establishment of one of the earliest Christian states. His construction of obelisks and inscriptions on stelae detail his exploits and affirm his Christian faith.