Alejandro Herrera, along with his sister Maya, are attempting to reach the United States from Guatemala in order to find Chandra Suresh in New York City (not knowing at the time that he was deceased), who they believe might be able to cure Maya's power to release a deadly virus onto everyone around her when she's upset. Only he has the power to reverse its effects.
Despite the fact that his sister Maya's deadly power was responsible for the death of his wife on the day that they were wed, Alejandro still decided to help his sister in her quest to America to have her power which she thought was an illness or a curse, inspected by Mohinder Suresh. After finding Sylar, Alejandro was skeptical of the man and got into a few confrontations with him. One of those confrontations ended up in fists flying every which way. Later in season 2, after Maya decided to stay with Sylar, Alejandro confronted the power thief again, unexpectedly defeating Sylar by knocking him unconscious.
Alejandro's ability is to neutralize the effects of an ability, but he uses this to neutralize his sister's ability. Alejandro and Maya thought that he was the only way to stop Maya's ability, but with the help of Sylar, she learned to neutralize her ability without Alejandro's help.
Alejandro's ability is somewhat shrouded in mystery. There are a few theories as to his ability and the extent of its potential. The theories are
1. Power Immunity - complete immunity to the abilities of advanced humans
2. Power Absorption - this theory shows that his ability is able to drain an active ability of an advanced human while suffering no ill effects from said ability
3. Power Immunity and Absoprtion - this mixed theory states that he is immune to the abilities of other advanced humans and also can absorb an active ability by direct physical contact (as shown with Maya Herrera)
The truth may never be known, as he was murdered by Sylar using a knife before the extent of his powers could be seen.
Before Alejandro was killed by Sylar, he started to speak perhaps the only English he knew.