Growing up in the nineties Sierra was everywhere and I played a lot of their games. Still, whenever I hear of them the first thing I think of is Half-Life. Which is especially funny considering how the lawsuit between Valve and Sierra/Vivendi contributed to the end of Sierra.

For anyone interested it's detailed from Valve's point of view in the Half-Life 2 documentary:

https://youtu.be/YCjNT9qGjh4