Terrorist Leaders planned and executed two terrorist attacks against targets in 2183 CE. One of the attacks was against the freighter MSV Ontario, owned by Martin Burns, the chairman for the Alliance Parliamentary Subcommittee for Transhuman Studies. The Subcommittee had denied reparations for L2 biotics that were suffering complications from their implants. A News Story is heard while on the Citadel about the kidnapping and the leader planned to use force to get their demands heard.
The other attack was against a Sirta Foundation base on the planet Chohe. Terrorists hit the facility with a hallucinogenic drug and are using the scientists as human shields. Admiral Hackett contacts Commander Shepard to ask for help in resolving the situation.
Terrorist Leaders are much more of a threat than their underlings. They carry shotguns and assault rifles in addition to pistols. Their biotics are more potent and can keep you down longer. They also have access to the Barrier ability, which is much stronger than their underlings as well. To keep these guys off balance, keep in cover, use biotics against them, and just keep shooting, and they will fall.