This guide will inform you of how well known certain races are and why this is so at a quick glance. This can be handy for many different situations, such as adequately determining if your character would know about them. Knowing obscure trivia of an obscure race would likely have some backstory involved to explain their knowledge. Keep in mind that a lot of familiarity depends on if a planet has connections to outside civilizations. A super famous race would still be unheard of on many planets without these proper connections. Therefore, "throughout the galaxy" would imply any planets around the galaxy that has an adequate connection to others.
The levels of popularity are as follows:
Legendary - A household name throughout most of the galaxy for many generation to come. If you've never even heard of them then you're probably on the planetary equivalent of living under a rock.
Famous - Not as well known as legendary on average but are still reasonably expected to be known by anyone even remotely close to them. People outside of their spheres of influence might known them as, "oh yeah, those leader guys of that place over there, right?" so might not have quite as much knowledge of them. Within their general vicinity yet hardly knowing anything about them would certainly raise eyebrows.
Well-known - Anyone within their alliance or near them would likely know about them, but outside of this would find the knowledge more sketchy than the above levels. Halfway across the galaxy and the average educated person might say they remember hearing about them only very rarely.
So-So - People in their alliance or near them may or may not know about them, and certainly not as much as the above levels on average. You wouldn't raise eyebrows one way or another upon knowing or not knowing them. Those on the outside could easily get by without hearing about them more than a couple times in their lives.
Obscure - People likely only know about them by being close to them or very educated in their alliance so makes a point to know about them.
Unknown - Virtually nobody else knows of the race.