Wikipedia: Eleazar and אלעזר הכהן.
Eleazar was the 3rd of Aaron's four sons. Served as the High-Priest after his father's death, because his older brothers had died.
Third son of Aaron (Ex. 6:23); admitted to priestly office (Ex. 28: 1). Eleazar and Ithmar were Aaron's chief assistants after the death of Nadab and Abihu by fire (Lev. 10: 12, 16; see also Num. 20: 25-29; Deut. 10:6; Josh. 14:1; 24:33). All the high priests until the Maccabaean period were descended from Eleazar, with the exception of those from Eli to Abiathar, inclusive, who belonged to the family of Ithamar.
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One of Aaron's sons and Moses' nephews, Eleazar was, like his three brothers and his father, a commissioned priest. After his brothers, Abihu and Nadab, suddenly died for their disobedience to God, Eleasar and his surviving brother, Ithamar, moved up to be chief assistants to Aaron. Later, on Aaron's death,j Eleazar became chief priest. He helped Moses in his census and Joshua in dividing the land of Canaan amoung the conquering tribes. Eleasar was the ancestore of all high priests until 168 B.C. except for a brief period in the time of Eli and Solomon. Exodus 6:223--25; 28:1; Leviticus 10; Numbers 3;; 4:16;; 16:37--39; 19:3--4; 20:25--26; 25:;7--11, Numbers 26,27,31,32,34; Deuteronomy 10:6; Joshua 114:1; 17:4; 19:51; 21:1; 22:13--32; 24:33; Judges20:28; I Chronicles 6,9,24; Ezra 7:5. - Everyone in The Bible.