Brian Epstein

Brian Epstein was the manager for The Beatles.

He managed The Beatles from 1962 until he died of an overdose in 1967.

Influence on The Beatles' early years
Brian was the one who suggested that The Beatles wear vests and dress shirts instead of leather jackets during their Cavern years. He also suggested they get ducktail haircuts instead of pompadours.

Influence on The Beatles on The Ed Sullivan Show and tours
Brian was the one who brought up the idea of The Beatles bowing in unison after each song when they preformed live.

He also got them to wear suits and jackets on The Ed Sullivan Show.

Death
Brian died of a drug overdose in late 1967.

The Beatles never did get over the loss.

Sexual Orientation
People have speculated that Brian Epstein was gay.

John did figure it out in early 1964 but he and Brian kept it a secret as homosexuality was then unheard of in England.