Read Gen 6 the sons of god were fallen angles they mated with the daughters of men their off spring were giants. There was a second influx of these fallen angels after the flood also resulting in giants. Here are some verse's you can study this,Also sons of godas you will read in Job had Satan along when going before the lord. Angels often take the form of men.Job 2:1 Again there was a day when the sons of God came to present themselves before the LORD, and Satan came also among them to present himself before the LORD this shows these were clearly not men. Gen 6:4 There were giants in the earth in those days; and also after that, when the sons of God came in unto the daughters of men, and they bare [children] to them, the same [became] mighty men which [were] of old, men of renown. --------------------------------------------------------------------------------Num 13:33 And there we saw the giants, the sons of Anak, [which come] of the giants: and we were in our own sight as grasshoppers, and so we were in their sight. --------------------------------------------------------------------------------Deu 2:11 Which also were accounted giants, as the Anakims; but the Moabites call them Emims. --------------------------------------------------------------------------------Deu 2:20 (That also was accounted a land of giants: giants dwelt therein in old time; and the Ammonites call them Zamzummims; --------------------------------------------------------------------------------Deu 3:11 For only Og king of Bashan remained of the remnant of giants; behold, his bedstead [was] a bedstead of iron; [is] it not in Rabbath of the children of Ammon? nine cubits [was] the length thereof, and four cubits the breadth of it, after the cubit of a man. --------------------------------------------------------------------------------Deu 3:13 And the rest of Gilead, and all Bashan, [being] the kingdom of Og, gave I unto the half tribe of Manasseh; all the region of Argob, with all Bashan, which was called the land of giants. --------------------------------------------------------------------------------Jos 12:4 And the coast of Og king of Bashan, [which was] of the remnant of the giants, that dwelt at Ashtaroth and at Edrei, --------------------------------------------------------------------------------Jos 13:12 All the kingdom of Og in Bashan, which reigned in Ashtaroth and in Edrei, who remained of the remnant of the giants: for these did Moses smite, and cast them out. --------------------------------------------------------------------------------Jos 15:8 And the border went up by the valley of the son of Hinnom unto the south side of the Jebusite; the same [is] Jerusalem: and the border went up to the top of the mountain that [lieth] before the valley of Hinnom westward, which [is] at the end of the valley of the giants northward: --------------------------------------------------------------------------------Jos 17:15 And Joshua answered them, If thou [be] a great people, [then] get thee up to the wood [country], and cut down for thyself there in the land of the Perizzites and of the giants, if mount Ephraim be too narrow for thee. --------------------------------------------------------------------------------Jos 18:16 And the border came down to the end of the mountain that [lieth] before the valley of the son of Hinnom, [and] which [is] in the valley of the giants on the north, and descended to the valley of Hinnom, to the side of Jebusi on the south, and descended to Enrogel, --------------------------------------------------------------------------------Job 1:6 Now there was a day when the sons of God came to present themselves before the LORD, and Satan came also among them.--------------------------------------------------------------------------------Job 2:1 Again there was a day when the sons of God came to present themselves before the LORD, and Satan came also among them to present himself before the LORD.--------------------------------------------------------------------------------Job 38:7 When the morning stars sang together, and all the sons of God shouted for joy?