behma, Hebrew, means predator, a kind of monster. It is mentioned in the Jewish Tanach, which is also is part of the bible. He is the first creation of God.
Job 40:15-24 King James Version (KJV)
15 Behold now behemoth, which I made with thee; he eateth grass as an ox.
16 Lo now, his strength is in his loins, and his force is in the navel of his belly.
17 He moveth his tail like a cedar: the sinews of his stones are wrapped together.
18 His bones are as strong pieces of brass; his bones are like bars of iron.
19 He is the chief of the ways of God: he that made him can make his sword to approach unto him.
20 Surely the mountains bring him forth food, where all the beasts of the field play.
21 He lieth under the shady trees, in the covert of the reed, and fens.
22 The shady trees cover him with their shadow; the willows of the brook compass him about.
23 Behold, he drinketh up a river, and hasteth not: he trusteth that he can draw up Jordan into his mouth.
24 He taketh it with his eyes: his nose pierceth through snares.
If you are familiar with cabbalistic teachings: You can interpret that Behemoth is the first being outside of God. He is the one who came into life with the first act of creation, with God limiting himself. So you can say Behemoth is the first evil, the first ‘dark’ God and he has many names.