Gen. Ali Mohsen al-Ahmar was the most powerful figure in Yemen’s military until he broke ranks with Saleh in March to support the protesters, vowing to protect them. He was one of the country’s top military commanders, a big supporter of Saleh (a WikiLeaks cable described him as Saleh’s “iron fist”), and was a member of Saleh’s Sanhan tribe.
Gen. Ahmar is not a member of the powerful Ahmar family, but he is said to be a half-brother of Saleh. Any familial loyalty that existed may have been broken last year. In Yemen, it's widely believed that Saleh tried to trick the Saudis into killing Ahmar.
In a US diplomatic cable released by Wikileaks, US Ambassador to Saudi Arabia James Smith recounts a conversation with Khaled bin Sultan, Saudi Arabia's assistant minister of defense and aviation, in early 2010.
The Saudis at the time were bombing Houthi rebels in support of Saleh, often with intelligence provided by his government. One mission was aborted by the Saudi pilots involved at the last minute because it didn't feel right. Prince Khaled told Mr. Smith that a Saudi investigation found that the coordinates provided were in fact Ahmar's headquarters.