Mordin Solus is a quirky Salarian companion to the player during Mass Effect 2 and 3. While some players love him for his brilliant mind, love of opera, and moral fortitude, others find it hard to overlook his shady past and dangerous research. Regardless, Mordin is able to sleep at night because he truly believes that every decision he makes is for the greater good.

Mordin is outwardly friendly and a good conversationalist, but he wears his past on his face in the form of scars from his days as a member of the Salarian military. Whatever your personal opinion is, consider these ten reasons why so many gamers consider Mordin to be Mass Effect’s greatest companion.

10 He’s A Brilliant Scientist

Doctor Mordin Solus is a brilliant and experienced geneticist. Though he’s never taught in a classroom, his Cerberus Dossier labels him ‘The Professor’ due to his expertise in his field and the teams of people who have worked under him on scientific projects.

The last research that he performed for the Salarian government was to study the genophage, a biological weapon released years ago on the Krogan in order to limit their reproductive rates. Mordin is always there to explain complicated scientific mumbo-jumbo to Shepard when it’s called for.

9 He Has An Excellent Singing Voice

Mordin might seem like the stuffy academic type, but that doesn’t mean he can’t have fun! So long as “fun” means “singing Salarian Opera.” When Mordin joins Shepard’s crew during Mass Effect 2, he reveals that he used to perform Gilbert and Sullivan.

Of course, it’s been slightly updated seeing as how it’s been hundreds of years since it was first released. The Major-General’s song is now about a “scientist Salarian.” He clearly regards those old memories fondly; he can be heard humming the song to himself if he dies at the end of Mass Effect 3.

8 He’s A Fan Of Film-Noir Movies

Mass Effect 3: Citadel was a DLC pack for the game released in March 2013. In it, Shepard gets a chance to explore new parts of the Citadel base and have new conversations with familiar characters from the series. If Mordin died while trying to cure the genophage, or was talked down from trying, he leaves Shepard a datapad to find in the Citadel.

Mordin narrates one of the stories on it with a voice-over like a film noir movie and includes himself singing scientific lyrics to the tune of familiar songs. Since he’s fond of Gilbert and Sullivan, it’s not such a stretch to assume he’s an all-around theatre buff.

7 He Plays Matchmaker

Mordin gets to know the crew fairly well from patching them up every time they return to the ship after another fight. With all that personal knowledge and trust, he takes an interest in pairing up crew members into romantic relationships. When Shepard enters a romance with a companion, Mordin offers advice (personal or biological, depending on Shepard’s choice).

He also helps Joker in his pursuit of EDI and can be overhead recommending “strengthening exercises” in preparation for EDI’s inflexible body. The most amusing is when he attempts to match Garrus with Eve, the Krogan woman who is meant to help save the species from the genophage.

6 He’s A Former Member of the Salarian Special Tasks Group (STG)

Salarians are a pretty advanced species in the Mass Effect universe, known especially for being excellent scientists. However, that doesn’t mean they don’t still need a military to protect themselves.

A large part of the Salarian military is the Special Tasks Group (STG), which takes on espionage missions at the command of the Citadel Council (since Salarians tend to gather intelligence before making any moves). Mordin worked for them for years as a scientist, earning combat experience as well as intel and contacts.

5 He Served Under Captain Kirrahe

In the first Mass Effect, the mission to Virmire is a huge story beat that players remember long after they’ve shut off the game. When Shepard arrives, they meet with a Salarian team already on the ground who have been tasked with investigating the planet and Saren’s base there. That team’s leader is Captain Kirrahe, a brave man who leads the charge.

Mordin notes that he served under Captain Kirrahe during his time as a part of the STG. He and the player remember fondly Kirrahe’s tendency for rousing speeches, and his oft-repeated phrase, “hold the line!” Even in Mass Effect’s enormous universe, it’s a small world. Moments like this with Mordin bring it to life in the hearts of its gamers.

4 He’s Also A Doctor

Once Mordin left the STG, he built a clinic on Omega for the people there; healing people was easier and came with fewer ethical problems than the work he had been doing for the Salarian military. The people living on Omega were often poor, and in desperate need of medical attention that they’d just been postponing as long as they could.

When Mordin joins Shepard’s crew, he’s an asset; changing the world is fun and all, but it comes with a lot of bullet wounds and broken bones.

3 He Works On The Crucible Project

The Crucible is a superweapon, designed by the Proteans for use against the Reapers, but they were wiped out before they could complete it. When Shepard recovers the Crucible plans during Mass Effect 3, building it becomes the utmost priority.

Obviously, Mordin’s brilliant mind is best put to use on the most important project. If he is convinced not to cure the Genophage, the Salarian race offers their official support to Shepard’s cause, and Mordin gets to work on the Crucible.

2 He Can Be Quite Ruthless

Mordin’s time in the STG taught him to do things by the book (and how to get around red tape when he needed to). Mordin’s time on the space station Omega proved he could fend for himself. Omega is a space station that’s a haven for criminals, terrorists, and malcontents, with no central government.

The good doctor fit in surprisingly well. He simply killed the Blue Suns or Vorcha mercenaries that got in his way, until they got the message and started avoiding him. Even Aria T’Loak, Omega’s “Pirate Queen,” admired his casual ruthlessness.

1 He Cures The Genophage

The genophage, released on the Krogan years before the first Mass Effect game began, makes it incredibly difficult for them to have children. Though the species has still managed to survive, the physical and mental damage have left a scar on the culture that has fragmented their society. When Mordin worked for the STG, he participated in the modification of the genophage.

By the time of Mass Effect 3, he is ready to atone for his mistakes. Unless Shepard talks him out of it or uses a Renegade interrupt to shoot him, Mordin is able to release a cure for the genophage by utilizing research performed by multiple scientists over the past few hundred years. The doctor dies in the process, but he allows uncountable Krogan to survive.

NEXT: Mass Effect: 10 Reasons Liara Is The Best Companion In The Trilogy