It was by King David:-
Psa 133:1 David.> Behold, how good and how pleasant it is for brethren to dwell together in unity!
Psa 133:2 It is like the precious ointment upon the head, that ran down upon the beard, even Aaron's beard: that went down to the skirts of his garments;
Psa 133:3 As the dew of Hermon, and as the dew that descended upon the mountains of Zion: for there the LORD commanded the blessing, even life for evermore.
Dr John MacArthur in "The MacArthur Study Bible" says
the occasion [my italics] for this Davidic psalm is unknown. Perhaps it was prompted by the nation's coming together in unity at his coronation....It's teachings on fraternal unity would have been instructive to [his] sons, who were antagonistic to one another...
The book of Psalms as it stands today was made by King David (Talmud, Bava Bathra 14b), but Psalm 139 was first spoken by Adam.
According to tradition it was written by King David, as were most of the other unnamed Psalms.
Psalm 19 is written by David.
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David wrote Psalm 38 through Psalm 47 :)
The bible does not mention it, but it is a Psalm of praise.
David
Psalm 28 was written by King David.
The Psalm 32 was written by king david.
Leonhard Widmer wrote Swiss Psalm.
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David
David
King David wrote Psalms 27.
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saul