[3] By 1934 Andreani had obtained Mexican citizenship and made his professional wrestling debut in 1934, taking the ring name "Jack O'Brien".

[4] After losing the lightweight championship O'Brien moved into the Welterweight division, probably the most prestigious weight class in Mexico at the time.

On November 23, 1941, Jack O'Brien defeated Lobo Negro to win the Mexican National Welterweight Championship.

[5] After the loss of the Welterweight title O'Brien began a long running, very successful storyline feud with El Santo and Gory Guerrero, the team known as La Pareja Atómica ("The Atomic Pair").

In 1952 O'Brien appeared in his first Lucha film as he both acted and wrestled in the movie Huracán Ramírez, he was also one of the men that found Daniel Garzia to fill the role of the title star.

He later retired from promotion when he was offered a government job in Cuernavaca, Morelos by the newly elected governor, who was a college friend.