They forgat God their Saviour ... - The God who had saved, or delivered them, out of Egypt. The sentiment here is the same as in Psalms 78:11-12. See the notes at that place.
Related Commentaries of Psalms 106:21
Psalms 106:21-22
21 They forgat God their saviour, which had done great things in Egypt;
22 Wondrous works in the land of Ham, and terrible things by the Red sea.