There are many stories of Rickson Gracie manhandling and submitting BJJ world champions when they came to visit him in his academy  during the 90’s.

One of the names that come up are bjj greats Fabio Gurgel and Roberto Traven.
These two were interviewed and asked about their experience training with the master, and they were very huble about it:

Interviewer: Do you still study with Jacaré?

Gurgel: Yes, whenever I come to America. Jacaré is a master of Jiu-Jitsu, and there is still much he can teach me. He has a school in Miami now and teaches there. Whatever I learn from him, I take back to my own schools in Brazil. I have four of them in different cities with over 700 students. Because Jacaré is one of my teachers, my schools are still associated with him.

Interviewer: You said “one of my teachers.” Do you have another?

Gurgel: Yes, Rickson Gracie. I studied with him also in Brazil and have been coming to Los Angeles, off and on, for nearly eight years to take lessons.

Interviewer: That’s a long way to study with just one man.

Gurgel: (laughs) Rickson is more than just one man—he feels like 5 when you’re fighting him. You have to sacrifice, sometimes, to study with the best, and Rickson is the best. I feel lucky, really. In the entire history of the Gracie Family, there have been many wonderful fighters, but only four “great” champions: Helio, Carlson, Rolls, and Rickson. I’ve been (associated) with two of them. One directly (Rickson) and one thru Jacaré (Rolls).

Interviewer: What’s it like training with Rickson?

Traven: (breaking in, laughing) Very humbling.

Interviewer: What is the one thing you’ve learned most from wrestling Rickson?

Traven: (still laughing) How to tap out. I’m getting very good at it.

Gurgel: (laughing also) With Rickson you have to learn to tap many different ways since your arms are often not free: the nose tap, the ear tap, the elbow tap . . .

Traven: Don’t forget the eye tap—blink three times fast.

Henry Akins, one of Rickson’s black belts described the first time that Rickson trained with Roberto Traven:

It was in the mid to late late 90’s (97 or 98 maybe) at the Pico academy when Fabio Gurgel came to town with several black belts from Brazil. One of the black belts that came with him was Roberto “Spider” Traven. I believe Roberto was a world champion black belt at the time or won the world’s shortly after this visit.
I remember seeing Rickson train with all the black belts, and doing what he normally does to them all, which is submit them multiple times within a 5-6 minute roll, but with Roberto he could not even pass his guard. You see this was the first time any of us had been exposed to the Spider guard, named after Roberto. Gripping the sleeves and using his feet in the biceps to create space and hold Rickson off, even though he was not able to sweep Rickson, I could see Rickson was very frustrated trying to pass his guard and eventually time ran out.
The next day they all showed up at the academy to train again and Rickson went with Roberto first. Those of us that saw what happened the previous day knew Rickson was frustrated and wanted another go. This time he passed his guard multiple times and submitted him with ease…. I was BLOWN AWAY!

We had all expected it to be another tough and frustrating roll for Rickson. How could things of changed so much in just one day? I asked one of the other instructors in disbelief what he think happened, whether Rickson was taking it easy the first day or not. He said “Rickson was pissed when he left yesterday, so I know he was thinking about it non-stop all night”.
Because of his deep level of understanding of the concepts and ideas of Jiu-Jitsu he went home and thought about what was going on and the problems this new guard was giving him THEN figured out how to deal with it and crush it. It was something none of us had seen or experienced before and in one day, because of his passion, determination, and mindset Rickson was able to come up with a solution.