Not P but DFW on politics

[Mike Jing]

The following excerpt is from David Foster Wallace's Up Simba:

It is Jim C.’s custom always to say “Up, Simba” in a fake-deep bwana voice
as he hefts the camera to his right shoulder, and he and Frank C. like to
do a little pantomime of the way football players will bang their helmets
together to get pumped for a big game, although obviously the techs do it
carefully and make sure their equipment doesn’t touch or tangle cords.

What's a "bwana voice" exactly? And where does the "Simba" reference come
from?