Mordin Solus is a brilliant scientist and doctor as well as a former STG Operative (Salarian Special Forces) who is easily recognized by his fast speech and logic above all attitude. Mordin is partly responsible for the continuation of the genophage, the devastating biological weapon that sterilized the entire Krogan race.
Originally he was on a research team sent to only study the effects of the genophage, when they then discovered that the Krogan was slowly developing a natural resistance to the virus Mordin helped develop a new and stronger virus to keep the genophage going at an "acceptable" level.
This was something that would weigh increasingly heavy on Mordin's mind as time moved on, unused to questioning his own decisions Mordin decided to set up a medical outpost on Omega hoping to find some peace of mind by focusing on healing people for a while. This is where he met Commander Shepard who then recruited him for the "suicide" mission against the collectors.
Mordin Solus was created by Bioware as a companion character for the player in the video game Mass Effect 2. He was voiced by Michael Beattie.
Mass Effect 2
Mordin had a big role in the events of Mass Effect 2 as one of the players main companions.
Mass Effect 3
Mordin also appears in Mass Effect 3, although his role is not as big as in the second installment.