In a recent biography, Alan Harrison notes that Toland was christened a Catholic with the name Janus Junius. Toland himself was the origin of this assertion as reported by des Maizeaux; but Harrison suggests it is more likely he was christened Seán Eoin. Both these names occur in Irish and derive from different forms of John: Seán from the Norman-French Jehan and Eoin from the Latin Johannes. While distinguishable in Irish, the two names become identical in English: John John. Harrison concludes accordingly that Janus Junius ‘may be an elaborate verbal joke on Toland’s part, echoing the anglicized version of his own name and at the same time indicating qualities he considered important in his personality: Janus the two-faced god (very much a trickster symbol incidentally) indicating his propensity for looking at things in more than one way and for his sayings to be capable of more than a simple literal interpretation; and Junius recalling the name of Junius Brutus, the reputed founder of the Roman Republic which in terms of political philosophy, was Toland’s ideal period’.
Richard Kearney writing on John Toland.
Postnationalist Ireland (1997). Chapter 10: “John Toland; An Irish Philosopher?” p. 131.