!) Sakumo is old enough to have known Tobirama given that at the time of his death he was older if not the same age as Hiruzen. Thus making him old enough to have been taught the jutsu by Tobirama.
2) Sakumo Hatake fulfills the 2nd point of my formula with the following scan, inwhich you not only see that Minato knew Sakumo but showed detailed knowledge of what happened and baased on the story he tells he seems to sympathize with him.
With everyone turning on Sakumo one wonders why Minato didn't. Perhaps there was a relationship there, Teacher and Student even? Not to mention that he also wound up taking up his son as his pupil.. coincidence?
Dive into it a bit further and we see a kind of pattern here. White Fang teaches Minato, who teaches Kakashi (White Fangs son), who teaches Naruto (Minato's Son). In both cases the fathers die prematurely leaving the sons to fend for themselves at a young age and in both cases the sons forgive there fathers. Both fathers are regarded as heros and both sons regarded as prodigies carrying on there fathers legacy. The same legacy which wasnt acknowledged at first. In Naruto's case he did not know Minato was his father, in Kakashi's case he did not want to be seen as Sakumo's son.
3) Now before I talk about the Lore of the infamous "White Fang" I would like you to take a look at the following scans:
In the scans above we see 3 things that point to the fame of the "White Fang"
- Chiyo seems to know the "White Fang" so much that she could recognize his face in kakashi decades after his death. So much so that she was willing to kill him on sight. This speaks to the power and the fame of the "White Fang"
- Oonoki recognized the last name "Hatake" as belonging to Sakumo and so when Gaara spoke of Kakashi Hatake Oonoki instantly questioned whether the two are related.
- Once again upon hearing the last name "Hatake" The firelord states that he must be the son of the "White Fang"
- The "White Fangs" fame was even so much that the Iwakagure Ninja hesitated to attack Kakashi after realizing that he might be his son.
The main thing here is that these are all extremely powerful Shinobi, people who dont take the time to remember the names of Shinobi that are up to snuff. And each of them have never forgotten the "White Fang". This speaks to how strong he must have been for his name/fame to have not only be so widespread but so everlasting. But does that remind you of anyone else???