Here's the story of an unsung hero
All of you have or will see him at least once in your playthrough
You almost never realize though because you kill him the first chance you get
he is the ADVENT Trooper

While retrieving supplies in a city filled with lost, The ADVENT trooper saw them get attacked
It was the horrendous XCOM
They had brought one of those foul Reapers and one of those Traitorous Skirmishers with them as well
Luckily the chosen assassin came to bless them with their presence and kill XCOM
She quickly took out the traitorous Skirmisher and another XCOM soldier was both injured and poisoned
All looked great for the ADVENT trooper
Until the reaper used a claymore on the assassin, who was weak to explosives and reapers
He believed the assassin would stay and continue the fight with them
She retreated however abandoning him and his friends to the lost and XCOM
and then he saw it
XCOM were saving their skirmisher ally
"How could this be?" He wondered
They risked so much for their ally, yet the greatest of ADVENT left him and his friends for dead
He had their poisoned and injured ally in his sights
When the time came he knew what he had to do
He ran in and drew the lost towards him, giving XCOM time to recover
Soon XCOM killed off the lost in the area leaving only him and them
He knew there was no way out of ADVENT except through death for him
He stood there waiting for the end
The Skirmisher then shot and freed him from the elder

Never forget the trooper who gave his life to save humanity

(If you liked XCOM 2 get this expansion)