The present name dates from the 17th Century, and as Moore argues probably derives from a draftsman's confusion in the 1609 grant of the Island to William, Earl of Derby.
That there were Bishops in Man from the earliest dates is clear from the little we know about the early Celtic church. Later there were Bishops of Man under the christianised Norse.
The present diocese arose with the erection of the see of Nidaros (today's Trondheim) which was already a place of devotion to Olaf. It would appear that Nicholas Breakspear (later Pope Adrian IV) was responsible for its erection during 1153/4 (the Papal Bull of Pope Anastastius IV is dated 1154). This erection which recognised the changed political climate, moved Norway away from the Archbishop of Lund (and prior to that Hamburg-Bremen) and created what must have been the most far flung see of its time as it covered Norway, Iceland, Greenland, the Faroes, the Shetlands and Orkneys as well as the Sudreys of which Man was the southernmost island.
As Mavor in his 1798 paraphrase of David Robertson's Tour of 1791, puts it
The see of the island is styled Sodor and Man. The first title has perplexed many. Camden derives Sodor from a small island, near Castletown, in which Pope Gregory IV erected an episcopal see; but this island has disappeared, or rather it never existed. It has likewise been alleged to have been taken from a village, in the Isle of I-Columb-Kill [Iona], where the bishop of the Western Isles had formerly his residence, or from Peel Isle in which are the remains of the Cathedral and the Bishop's palace; and which some say, obtained the appellation of Sodor after the English conquest but neither of these derivations is right...
It appears from the best authorities, however, that during the time the Norwegians were in possession of the Hebrides and Man, they divided them into two parts, distinguished by the appellation of the Sudereys and Norderys, or the islands lying south or north of their ideal line of demarcation. Afterwards a bishoprick of the isles was formed; but Man, as being the the ancient see, retained the title of Sodor, from the Sudereys, though its prelate lost all jurisdiction over the division of the isles so called.
In this derivation Mavor was correct, the name Sodor
being derived from diocesus Sodorensis the latinised
form of diocese of the Sudreys from the Scandinavian
Suðreyjar, the South Islands (i.e. the Hebrides
as viewed from Norway). (ð is
pronounced th as in father).
The map shows the maximum extent of the Kingdom of Man which may be considered to have started when Godred Crovan consolidated a kingdom there in 1079, and to have have formally ceased in 1266 when it was ceded to the King of Scotland following the Battle of Largs in 1263. Mull, Islay and Kintyre (the lighter shaded regions on the map) had already been lost to Scotland by 1156.
The Abbots of Bangor, Sabal, Whitehorn and Furness were barons of the Island.
Moore's history of the Diocese is probably the most comprehensive, though being now more than a century old, cannot reflect modern scholarship. In 1836 the Westminster parliament legislated to annex the Diocese to that of Carlisle (see map from 3rd Report) - a belated action by Bishop Ward was successful in getting this act repealed in 1839. Wm Wards 'Isle of Man and Diocese of Sodor & Mann' was put together in support of this action and contains many useful extracts of ancient documents.
William Harrison put together a collection of relevant documents in his 'An Account.'published by the Manx Society.
The most recent, and very readable, history of the Diocese is that by Canon Gelling which covers the period from Bishop Wilson (1698) through to early 20th Century.
For a list of post-reformation bishops see elsewhere.
D.S. Dugdale Manx Church Origins
Llanerch: 1998 (ISBN 1-86143-067-1) is an attempt to give some history of the Manx Church pre the formation of the Diocese.
J. Gelling A History of the Manx
Douglas:Manx National Heritage 1998
W. Harrison. An Account of the Diocese of Sodor
Manx Soc. Vol. XXIX. 1879
and Man (in Diocesan History
History of the Isle of Man 2 vols
London: T.Fisher Unwin 1900 (reprinted 1977 and 1992 by Manx Museum)
Else Roesdahl The Vikings
Penguin (0-14-012561-2) 1992
W.P. Ward Isle
of Man and Diocese of Sodor &
London: Rivington 1837
G.V.C.Young The History of the Isle of Man
under the Norse
Peel:Mansk-Svenska Press 1981