The name Cletus has its origins in ancient Greek, derived from the word "kletos" which means "called" or "renowned." It is a masculine name that became popular in early Christian communities.

In the New Testament of the Bible, Cletus is mentioned as an early leader of the Christian church in Rome, sometimes identified as the third Pope or Bishop of Rome after St. Peter and St. Linus. However, the historical details surrounding this Cletus are uncertain.

The name Cletus gained popularity in the early Christian era and was used by several saints and martyrs. One notable Saint Cletus was a 3rd-century martyr from Gaul (modern-day France) who was beheaded during the persecution of Christians under the Roman Emperor Aurelian.

The earliest recorded use of the name Cletus can be traced back to the 4th century AD, with references found in various early Christian writings and records. Among the notable historical figures named Cletus are:

1. Cletus of Brescia (d. 97 AD), an early Christian martyr and saint believed to have been executed during the reign of Emperor Domitian.

2. Cletus of Amasea (d. 304 AD), a Christian martyr from Amasea (modern-day Turkey) who was executed during the Diocletian persecution.

3. Cletus of Nicomedia (d. 312 AD), a Christian martyr from Nicomedia (modern-day Turkey) who was executed during the reign of Emperor Maximian.

4. Cletus of Alexandria (4th century AD), a Christian monk and writer from Alexandria, known for his treatise on the monastic life.

5. Cletus of Auxerre (d. 580 AD), a 6th-century Bishop of Auxerre in Burgundy, France, who is venerated as a saint in the Catholic Church.

The name Cletus has remained in use throughout the centuries, particularly in Catholic and Christian communities, although it has not been as widely popular as some other names of Greek or Latin origin. Its meaning of "called" or "renowned" has contributed to its enduring appeal as a name with a sense of distinction and significance.