The polar opposite of an alpha male.

Male in a group who is least likely to take the initiative and lead, due to a lack of esteem, ability or interest.

Antonym of "alpha male".

While alpha males and beta males compete, omegas hang back and watch or do whatever. Whatever is left after the alphas and betas are done they either take or leave. They can be the "cool" kids or "the nice guys who finish last."

omega is the last letter of the greek alphabet. alpha is the first letter. an omega male then is the "last" man. in essence, if you were to rank all the men in the world by their virtues (bravery, intelligence, leadership, generosity, etc.), an omega male altogether would be the worst, hence "last," of all men. none of these other definitions listed on here have much relation to the actual meaning of "omega male" - both as it's been used historically and as it's used currently, particularly the ones that list it as a positive quality and who don't seem to understand the significance of "omega." additionally, the word "omega male" usually refers to a category, rather than a single individual, of "last" men.
if someone says you're an omega male, they're literally saying that not just that every man on earth, save other similarly repugnant omega males, is better (i.e., more generous, braver, etc.) than you, but also, given being "last," that you don't really have these basic virtues at all. it's an insult, not a compliment.
contrast with: alpha male: (the first letter of the greek alphabet, hence "first" man.) effectively, an alpha male is first among men, the best of all men.
the alpha/omega rankings can be used with women as well and are, albeit less frequently.

Omega Male, is basically the servant male of the tribe. These terms, Alpha, Beta and alas Omega were used to designate hierarchy in the Ape community, but later were applied to human hierarchy as well. Omega Male is not necessarily the outside wise man or thinker as some are describing here. It's not that this male can't be wise, its just that he is often as likely to be powerless, maybe even slow as he is smart and internalized and relegated to the bottom rung of the ladder.
While the opposite of Omega is Alpha, this doesn't designate simple physical prowess and might as it does with Apes. Alpha does not crave attention or validation from others, that is normally a Beta trait of attempting to improve his station. Alpha just gets the attention. It can be leadership, smarts, ability to earn and of course physical confidence and might, which shows his potential mates that he can protect, provide and defend his family. See basic human attraction triggers.
Finally, since we are humans and not apes, Alpha/Omega isn't being the toughest man on the block.. Today Alpha is manifested in confidence, success, wit, and yes still some physical prowess. The modern Alpha is the man who is unafraid to speak his mind, unafraid to embrace his masculinity and also unafraid to defend his POV / loved ones / offspring. This is directly opposite to the man who would scurry away in fear at the first sign of confrontation, afraid to speak his opinion, unsure of himself etc.

A male who has reached peak misogyny, he hates women so much that he has become gay

An Omega Male is usually a being of pure masculinity. The polar opposite of a Soy Boy, the Omega Male always show's dominance in every situation. Often lacks empathy and sympathy towards anybody and anything. Likes girls, but disrespects women.