Chief Operating Officer to Explorers

From Into Africa: The Epic Adventure of Stanley and Livingstone, by Martin Dugard (Broadway Books, 2003), Kindle locs. ~400, ~2000:

Among their caravan was a hard-working young African named Sidi Mubarak Bombay, whom Burton referred to as “the gem of the group.” Bombay was a member of the Yao tribe who had been captured by Arab slave traders at the age of twelve, then sold in the Zanzibar slave market to an Arab merchant. When that Arab moved to the city of Bombay shortly after, his young slave came along. After his owner's death, the slave was given his freedom and the adopted name of his new hometown. Upon returning to Africa sometime in his early thirties, Sidi Mubarak Bombay joined the Sultan of Zanzibar's army as a soldier, and was posted to a garrison in Chokwe. That outpost seven miles from the Indian Ocean coastline was where Burton and Speke met up with the industrious, grinning former slave. By arrangement with the garrison commander, Bombay and five other soldiers were hired to accompany the British caravan. Bombay's work ethic and linguistic skills soon made him invaluable to Burton and Speke. Unbeknownst to Bombay, his soldiering career was at an end, replaced by a new line of work.

Bombay spoke fluent Hindustani, as did Speke, so Bombay served as Speke's gun bearer and translator. “He works on principal and works like a horse,” Burton wrote of the short ugly man with filed-down teeth and an aversion to bathing, “candidly declaring that not love of us but duty to his belly makes him work. With a sprained ankle and a load quite disproportionate to his puny body, he insists on carrying two guns. He attends us everywhere, manages our purchases, carries all our messages, and when not employed by us is at every man's beck and call.” Bombay would go on to become the talisman of African exploration, an essential roster member on any serious expedition for decades to come.

...

The legendary Sidi Mubarak Bombay—“the honestest of black men who served with Burton, and subsequently with Speke”—came on board as leader of Stanley's protective militia. In time, Bombay would serve as unofficial caravan leader, and liaison between Stanley and the pagazis [porters].

Thirteen years had passed since a young Bombay had dazzled Burton and Speke with his easy humor and insatiable work ethic. But he was still able to walk thirty miles at a brisk pace, had worked with the most expeditions of any man, and knew the interior by rote. Bombay, however, had also passed into middle age. He was bald and the young pagazis didn't respect him. As the rare man in history to follow the Nile from Lake Victoria to the Mediterranean, Bombay thought himself a celebrity. He had an ego, as Stanley knew from reading the works of Burton and Speke, and could be outspoken, prone to drinking and chasing women, and a procrastinator. So there were liabilities incumbent with Bombay's hiring. All in all, however, the exploration veteran was vital.

Stanley trusted Bombay so much he let the former slave hire his own soldiers. Bombay handpicked twenty men.