Game of Thrones: In the Beginning, I Take the Mad King to Escape from Stoddenburg!

After soul transmigrating to Westeros, he starts off locked in the same cell as the legendary Mad King, Aerys Targaryen II, and somehow gets appointed by the already half-mad king as a member of the Kingsguard.

.......

Aerys Targaryen: "Back then, I led Lancelot through seven charges in and out among thousands of enemy troops in Deepwood Motte, and never even blinked once!"

Barristan Selmy: "To be honest, I don’t know why, but I’ve always felt like I was living in Lancelot’s shadow."

Jaime Lannister: "Lancelot is a great and outstanding knight. I even saw him once urinate with his right hand while wielding a sword with his left, cutting down Arthur Dayne, the Sword of the Morning!"

.......

Many years later, Lancelot holds a greatsword in both hands, standing on the head of a dragon, sword tip pointed at the White Walker army below.

"Watch closely, you ice-shedding blue bastard."

"This sword strike will be very cool!"