Probably a clown trigger (Balistoides conspicillum )(black with yellow/white spots)
Triggers are very agressive (try keeping an undulate trigger

). They will attack fish, eat crustaceans with their powerful bone crushing jaws, throw live rock around the tank and generally cause mayhem!
I have seen an undulate kill itself by biting through a heater and electrecuting itself

I also saw the damage a clown trigger did to a tank when it charged the glass and put a crack in it.
While these horror stories might put many aquarists off, triggers are actually wonderful fish to keep. They can swim backwards almost as fast as they can fowards, always active and exploring the tank etc.
Although triggers are regarded as generally aggresive and kept alon or in species tanks, some are actually very peaceful and reef safe!
I have 2 such triggers in my reef tank and they cause no trouble at all.
These 3 spieces are:
Xanthichthys Ringens (Sargassum Trigger)
Though it will not touch corals, small shrimps might be at risk, fish are safe however and it can be kept in small groups with ease in an aquarium.
Odonus Niger (Niger/Blue/Black/Red Tooth Trigger)
This grows very large and is another Reef safe fish. I have one of these in my tank. Very bold and highly inquisitive, can be a bit bullyish but doesnt cause any harm, he just likes the others know he is top dog in the tank
Xanthichthys Auromarginatus (Blue Throat Trigger)
This is my favorite Trigger

I have a male in my tank and i could not ask for a more peaceful and reef safe fish! HE tends to be very shy and never shows any signs of aggression (he even ran off and hid when he saw his reflection in a mirror

) He shares a cave in my tank with a small group of Blood shrimps. He even allows these shrimps to crawl all over him to clean him etc.
This is also one of the smaller species of Triggers so its more suited to a home tank. There are basically 2 types of triggers. Reef hunters and open plankton feeders. Nigers and Bluethroats tend to spend their time feeding on plankton that rise up from deeper waters near reef edges. Whereas Undulates and clown triggers etc spend their time hunting for crabs, lobsters and other prey (seems they like a challenge

)
Hope this helps give a little insight into triggers, great fish! and one that many people dont think they can keep.