Imperial Hydra was a SHIELD villain, and the leader of HYDRA.
Not much is known about Arnold Brown's past. He became Imperial Hydra of the subversive organization known as HYDRA. When his wife died in poverty, Brown promised that he would give his daughter, Laura everything that his wife had lacked. It's unknown when Brown joined HYDRA, all is known is that he joined HYDRA after his wife died. Brown worked his way up the ranks in HYDRA, until, he became Imperial Hydra. Brown used his position to divert money and resources secretly to HYDRA.