Hymn No. 68, A Mighty Fortress Is Our God -- Ein Cadarn Dŵr Yw Duw a'i Rad

The LDS version has only one verse and emphasizes the power of God rather than the forces of darkness. I took the first two lines from the first verse in Welsh and the rest of the lines from the second verse in Welsh to more closely match the LDS version in English.

The Welsh source was found here.

Ein cadarn dŵr yw Duw a'i rad,

Ein tarian a'n hamddiffyn

Ond drosom mae'r addasaf Un,

A Duw ei hun a'i trefnodd.
Pwy yw? medd calon drist;
Ei enw_yw Iesu Grist,
Tywysog lluoedd nef,
Ac nid oes neb ond Ef
  A lwydda yn yr ymgyrch.