We greet each other with a hearty "Ya Ali Madad" everyday and you see faces light up immediately but have you wondered at the history and significance of this greeting?
Even though I do not have access to scholarly texts or reference material at my disposal, I'll make a humble attempt of my own understanding of this piece of history, from oral traditions, general knowledge, web sources and, of course, my personal experience in invoking this . If anyone has a more detailed account or analysis, I'd really appreciate your contribution.
As we all know, (a.s.) was the first male Muslim convert (Hazrat Khatija being the first female believer) and he took up the responsibility to propagate the Holy Message delivered to our beloved (s.a.s.) at a tender age. He was only twelve when Prophet Muhammad asked who would come to his help with this work at a family gathering at Abd-al Muttalib's (their grandfather) house. Hazrat Ali (a.s.) was the only one who stood up and declared his allegiance and offered full support for Prophet Muhammad's (s.a.s.) mission. The Prophet blessed Imam Ali (a.s.) and said, "From now on you are my helper, my Wazir and the Khalif after me on earth."
There were many other historical incidences where Hazrat Ali was always at the Prophet's side working to forward the cause of Allah. This meant not only educating the new Muslims about the fresh revelations but also defending the believers from the opposition to this new faith. Prophet Muhammad came to rely on Hazrat Ali's help as his chief commander of his army and with the help of his two-horned sword named Zulfiqar (which means 2-pronged), Hazrat Ali defeated many an army.
source : http://www.amaana.org