Short answers, pulled from the story.
Irenaeus was born in Smyrna, now İzmir, Turkey, during the first half of the second century, likely between the years 120 and 130. He grew up hearing the preaching of Polycarp, a bishop who had been a student of John the Evangelist.
The most famous work of Irenaeus is Against Heresies, a five-volume treatise written around 180. This work was designed to refute the teachings of various Gnostic groups and remains the best surviving description of Gnosticism until the discovery of the Library of Nag Hammadi in 1945.
Irenaeus was the earliest surviving witness to assert that all four canonical gospels, John, Luke, Matthew, and Mark, were essential scripture. He argued that the fourfold Gospel was necessary to counter the efforts of heretics like Marcion and Tatian, helping to establish the canon of the New Testament.
Irenaeus developed a theology of salvation that centered on the concept of recapitulation, where Christ is seen as the new Adam who systematically undoes what Adam did. He believed that the Incarnation of Christ was intended by God before the creation of humanity to restore humanity to being in the image and likeness of God.
Irenaeus argued that Jesus ministers while in His 40s and that He did not die until He was older than is conventionally portrayed. He used scripture to add several years to Jesus's ministry, citing three distinct visits to Jerusalem as evidence against the Gnostic claim that Jesus preached for only one year.
Irenaeus was declared a Doctor of the Church in the Catholic Church by Pope Francis on the 21st of January 2022. He was conferred the supplementary title Doctor unitatis, or Doctor of Unity, and his memorial is celebrated in the Latin Catholic Church on the 28th of June.