The Greeks and Romans originally did NOT venerate a God of the Sun.
The early Greeks—themselves—seemed to have venerated “Helios” from the Greek Titan pantheon, rather than the Greek God, “Apollo"/"Apollon” as a deity associated with the sun, light, heat, etc.
Arrows shot at mortals by Apollo/Apollon symbolized sudden death—and not only in Greece. Indeed, the motif of arrows shot at mortals by any supernatural beings commonly symbolized sudden death. Apollo’s/Apollon's far-reaching arrows could inflict plagues and epidemics on humankind. Although Phoebus Apollo was known for healing, his name could also be interpreted as meaning "destruction".
The Ancient Greeks most often associated Apollo's name with the Greek verb apollymi, "to destroy". On the other hand, Apollon was petitioned to provide aid in fending off plagues and other evils.
The Greek name Apollon does mean "destroyer". Apollon did slaughter or slay Niobe's children asserting that his mother, the minor Goddess Leto, was worthy to be known as a member of the Theoi (Gods). One must realize Leto was the mother of two powerful Theoi: Artemis (moon) and Apollon (sun). That meant Leto's children really were "the Sun and the Moon".
When the twins Artemis and Apollon took vengeance upon Niobe, who bragged about bearing Zeus seven daughters and seven sons, Apollon slew all of Niobe's sons with the Sun God's golden arrows. Then Artemis slew all of Niobe's daughters with her silver lunar arrows. These deities (Apollon and Artemis) purposely took vengenge upon Niobe, her seven sons, and seven daughters. It was punishment for Niobe's excessive pride or “hubris" regarding her own children.
Yet Apollon could also be the averter of evil. Apollon the Destroyer is the Theo (deity) who provides aid to "fend off evil", such as plagues.
Nevertheless, it was the Latin name "Phoebus Apollo" that seems to have become the most commonly used name to represent the Greco-Roman God of the Sun. I remember reading the name "Phoebus Apollo" in textbooks back in the 1970's.
It seems—and this is my guess—that during the Italian Renaissance, Phoebus Apollo came to be viewed as a God of “light” and “illumination” as well as a "God of Reason".
DO Gods CHANGE?
Well, those of us who study mythology know that our “somewhat limited human perception” of deities changes through decades and centuries of the stories being told and retold. Indeed, a modern Pagan once said, “The Gods are like whores” …meaning they will often be willing to do for us whatever we ask for—and however we somewhat carelessly word that request. Ideally, one ought to clearly and carefully word the petition.
Of course, any deity (Thea/Theo)--at any time--may just flat out say NO, and simply ignore the petition from a mortal.
Eventually it was Apollo who became the chief God of healing and the Sun—in the Greek Pantheon—supplanting and thus making the Titan “Helios” simply to be the God (Titan) who drove the Sun chariot across the sky daily.
So, my beloved reader, remember it was the Latin name “Phoebus Apollo” that became the most commonly used name of the Greco-Roman God of the Sun.
I would like to share a little more examination of the transliteration of the original Greek name "Phoibos Apollon".
“Phoibos” meant “Light”.“Phoebus Apollo” was the deity name adapted by the Romans for the Greco-Roman Sun God. It became the written form of this God's name most used in the 21st century, USA. As I stated previously, I remember reading "Phoebus Apollo" in text books way back in the 1970's.“Apollon” meant “Destroyer”.
Clearly, Gods (Theoi) DO change.
Here is a published contemporary written source of the “Apollon” spelling:
William Hansen, The Book of Greek & Roman Folktales, 2017, pp 10, 50, 61, 82, 89, 99, 129, 130, 231, 242, 311, 363, 364, 414.ADDED NOTE: There was only one other time that I have stumbled across this spelling of the name—“Apollon”—the Greek Sun God as transliterated from Greek into English.
It was around 1977-1978, and I had an English Teacher who wrote the spelling of “Apollon” on the chalk-board during a lecture on Greek mythology. He stated briefly that this was a less known English spelling of the name of the Greek Sun God. The teacher also said the name meant, “Destroyer.”
Myth Woodling, 9/17/2023
Sources
William Hansen, The Book of Greek & Roman Folktales, 2017.
Apollon, en.Wikipedia.org, accessed 9/14/2023. (Yes, I know Wikipedia is not a primary source and some people do not consider it credible. I have noted it here anyway.)
Theoi Sources
Please note that Theoi.com is considered a legitimate source by many scholars.
APOLLON (Apollo), www.Theoi.com, accessed 9/14/2023.Apollon, www.Theoi.com, accessed 9/14/2023.
twinkl.com Source
I have copied this note from a teaching site called twinkl.com.
apollymi meaning "to destroy"
"The name Apollo is still not properly understood, it's likely that it means 'destroyer' - at least that is what the Greeks take it to mean. But it could also stand for 'purifier,' 'assembler,' or 'redeemer.'" Apollo the Greek God, twinkl USA, accessed 9/14/2023