Johanan (or John Gaddi/Caddis in the King James Version, Hebrew: יוחנן הגדי) was the oldest of the sons of Mattathias, and brother of Judas Maccabeus. He was one of the leaders of the revolt of the Maccabees in the 2nd century BC.
First historical reference
He was first mentioned along with his father and brothers, in this way: "In those days Mattathias the son of John, son of Simeon, a priest of the sons of Joarib, moved from Jerusalem and settled in Modein. He had five sons, John surnamed Gaddi, Simon called Thassi, Judas called Maccabeus, Eleazar called Avaran, and Jonathan called Apphus." (1 Maccabees 2:1-5 RSV-CE)
Possible reference in 2 Maccabees
The next reference is in the Jewish historical work 2 Maccabees. It is as follows: "With these words he (Judas) filled them with good courage and made them ready to die for their laws and their country; then he divided his army into four parts. He appointed his brothers also, Simon and Joseph and Jonathan, each to command a division, putting fifteen hundred men under each. Besides, he appointed Eleazar to read from the holy book, and gave the watchword, "God's Help"; then, leading the first division himself, he joined battle with Nicanor." (2 Maccabees 8:21-23 RSV-CE) Just after this battle, as the Talmud, Josephus, 1 Maccabees 4:36-59, and 2 Maccabees 10:1-8; the brothers recaptured and rededicated the Temple of Jerusalem, starting the Festival of Dedication (or as it's more commonly known, Hanukkah.)
The final references to John Gaddi are the events surrounding his death. This is the account found in 1 Maccabees: "And Jonathan sent his brother as leader of the multitude and begged the Nabateans, who were his friends, for permission to store with them the great amount of baggage which they had. But the sons of Jambri from Medeba came out and seized John and all that he had, and departed with it. After these things it was reported to Jonathan and Simon his brother, 'The sons of Jambri are celebrating a great wedding, and are conducting the bride, a daughter of one of the great nobles of Canaan, from Nadabath with a large escort.' And they remembered the blood of John their brother, and went up and hid under cover of the mountain."' (1 Maccabees 9:35-38 RSV-CE)