I have quite a few ideas, if I'm honest. I'd definitely recommend doing research on the suggestions though to make sure that:
1) you like their appearance/behaviour
2) you can provide for them
3) if you decide to put more than one kind of fish together that they are good together
I'm sure you will, but just making sure that I put this here. I got screwed over once by a LFS guy that didn't quite know what he was doing. These are kind of the rules I have lived by ever since.
Anyways, my first suggestion is a Malawi Cichlid tank. Picking the right fish for you, in this case, would def require some research and work but they are relatively aggressive fish that are quite intelligent and appealing to the eye. Make sure to stick with fish right for your size of aquarium, some Malawi cichlids get really big.
Second suggestion would be mid-sized South American cichlids. My two favourites, appearance wise, are the Jack Dempsy (electric blue) and the Green Terror. You could possibly get yourself a single Oscar if neither of the above suggestions appeal to you.
Third suggestion would be to go for a Flowerhorn cichlid. While I have never had one myself, the ones I see (both in the LFS and on Youtuber vids) are extremely personable and friendly to people while still being a nice looking, aggressive fish.
Fourth suggestion would be some form of catfish. I don't know much about catfish, though I know that there has got to be some variety suitable to the 75 that matches the characteristic of being aggressive (if not in behaviour then at least in feeding). Catfish are greedy pigs.
Last suggestion would be Tanganyika cichlid. My personal favourites are Neolamprologus brichardi, they tend to not get too large so you could get several then let them breed up the tank population from there. I haven't had this one either but from what I have heard this fish gets super aggressive/protective after spawning. I've seen people talking on this site about how breeding pairs just dominate entire tanks or something like that. If not Neolamprologus brichardi; then Julis, Cylindricus, Compressiceps, and other Tangs are equally good options.