Mithras was worshiped as a primary deity during the Roman Republic and much of the Roman Empire, particularly in Byzantium.
There are possibly Hindu and Vedic origins for Mithras as a sun god as well. From an unspecified Vedic hymn 1
...he [Mithras] is invoked with
Ormazd, or Ahuramazda, the god of the
sky, and is clearly a divinity of
light, the protector of truth and the
enemy of error and falsehood.
This is a more specific reference 2
In Vedic hymns (Rigveda, III, 59), he [Mithras] is frequently
mentioned and is nearly always coupled
with Varuna, but beyond the bare
occurrence of his name, little is
known of him.
The Avesta was more specific than the Vedas, probably because the role of Mithras was more significant in the former. The Avesta is a religious text that is also associated with the rise of Zoroastrianism in Persia. It featured Ormazd as a major deity 1
His worship spread with the empire of
the Persians... their belief that the
legitimate sovereign reigned by the grace of
Ormazd, whose favour was made manifest
by the sending of the Hvareno, a
celestial aureole of fire, resulted in
the doctrine that the Sun was the
giver of the Hvareno. Mithras,
identified with Sol Invictus at Rome,
thus became the giver of authority and
victory to the Imperial House... the
Sun was the most important of
deities; and it was the Sun with whom
Mithras was identified.
Mithras probably originated in India. The belief spread, and expanded in scope, to nearby Persia. It continued westward over a period of many centuries, eventually making its way to ancient Rome, and lands that were part of the Roman Empire. This included Germany, and of course Britain. The religion declined in adherents very quickly as of 300 A.D. The historical record has remained intact though e.g. sculptures of Mithras as a sun deity survive through the present day in Rome, on the Capitoline Hill.
This was my rationale for conjecturing that Mithraism could be an antecedent for the expression "worshipers of the rising sun", and maybe for the association with worldly success.
1 Mithras: 1911 Encyclopedia Britannica
2 Arendzen, J. Mithraism in The Catholic Encyclopedia. New York: Robert Appleton Company. From New Advent.