Klāvs Siliņš: Latviesu personvārdu vārdnīca. Riga "Zinātne" 1990, ISBN 5-7966-0278-0
Population Register of Latvia: Uldis was the only given name of 7626 persons in Latvia on May 21st 2010.
Etymology
First recorded in the end of 19th century. From Ulrihs(“Ulric”), ultimately from Old High German. Name of a character in the play Pūt, vējini! (1913) by Rainis.