This is what we found on Wikipedia regarding the Manly Warringah Sea Eagles:

The Manly Warringah Sea Eagles are an Australian professional rugby league club based in Sydney's Northern Beaches. They compete in the National Rugby League (NRL). The Manly club debuted in the 1947 New South Wales Rugby Football League season and currently hosts the majority of their home games at Brookvale Oval in Brookvale. They train at their Centre of Excellence in Brookvale, and at the New South Wales Academy of Sport in Narrabeen. The team colours are maroon and white, and they are commonly known as Manly.

The club competed in the NSWRL, ARL, or NRL competitions in all respective seasons from 1947 until 1999. At the end of 1999, they entered into a joint venture with the North Sydney Bears to form the Northern Eagles, which rugby league statisticians regard as a separate club. The Northern Eagles competed in the 2000 and 2001 NRL seasons, after which the joint venture collapsed. The Manly Warringah club (who held the NRL licence) competed in the NRL as the Northern Eagles for a further season in 2002, before abandoning the name and identity to return to what they are known as today.

Since winning their first premiership in 1972, the club has won a further seven first-grade titles, with their most recent being in 2011. The club's eight titles span five consecutive decades. Since their first Grand Final appearance in 1951, the club has appeared in 19 Grand Finals across seven consecutive decades.