cardinal Giacomo Orsini

GIACOMO ORSINI, created cardinal-deacon by Gregory XI on 30 May, 1371, d. at Vicovaro or at Tagliacozzo, 1379. He was distinguished for his knowledge of the law. Appointed papal legate in Siena in 1376, he was a strong supporter of Gregory XI. In the conclave of 1378, he espoused the cause of Urban VI, but later attached himself to the antipope Clement VII.

[https://www.newadvent.org/cathen/11325b.htm]

Note on ROLE/TIT:LE Cardinal-Deacon

The cardinal deacons are the lowest-ranking cardinals. Cardinals elevated to the diaconal order are either officials of the Roman Curia or priests elevated after their 80th birthday. Bishops with diocesan responsibilities, however, are created cardinal priests.

Cardinal deacons derive originally from the seven deacons in the Papal Household and the seven deacons who supervised the Church's works in the districts of Rome during the early Middle Ages, when church administration was effectively the government of Rome and provided all social services. Cardinal deacons are given title to one of these deaconries.

Cardinals elevated to the diaconal order are mainly officials of the Roman Curia holding various posts in the church administration [ https://en.wikipedia.org/wiki/Cardinal_(Catholic_Church) ]