Osama bin Laden and a handful of the "Afghan Arabs" around him. That's who.
More complete explanation: While donors from Saudi Arabia and other Gulf Arab states - private and state ones, or at least, state-sponsored - certainly were generous in supporting Osama bin Laden and his "Afghan Arabs", it is important to remember had his own (personal and family) money as well. Remember, this was before he was disowned by his brothers and sisters - at least, officially - and so he had access to much more family money throughout the 1980s.
He also had a close relationship with Saudi intelligence at this time, and with important Saudi royals - perhaps especially the head of Saudi intelligence himself, Prince Turki bin Faisal. Whether those relationships continued right up to 9/11 to any extent, albeit covertly - even after he was overtly disowned by the Kingdom, exiled to Sudan and then Afghanistan, and stripped of his citizenship - is a matter of controversy to this day.
Additionally, Osama almost certainly had many contacts with Pakistani intelligence; at the very least, it is beyond dispute that he made several important friends among the most Islamist and extreme of the Afghan mujahideen commanders, many of whom were being funded directly by Pakistan (and Saudi Arabia, I suspect). Some of these people later had falling outs with bin Laden from what I understand, but others remained allies, and welcomed him into Afghanistan after he was run out of Sudan in 1996. Of course, the Taliban consolidated power in most of Afghanistan around this same time - and while most of the people who became the Taliban were in Pakistani refugee camps during the Soviet war in Afghanistan, they were later heavily nurtured and sponsored by Pakistan as the force to create some sort of stability and government in Afghanistan during the incredibly bloody Afghan Civil War that raged in the 90s.
As for the US and CIA: They (we, as an American here) were certainly heavily involved in the covert operations and financing of the Afghan mujahideen, and the Saudis were certainly matching CIA funds to the effort (and may well have provided even more), but all of this was being coordinated by the Pakistanis - specifically, the notorious ISI intelligence service. And the Saudis, as I previously mentioned, supported Osama bin Laden and his crew as part of their broader effort, and the Saudis, the Pakistanis,the mujahideen, the US, and indeed, Osama bin Laden were all playing on the same team in terms of fighting against the USSR in Afghanistan; yet the details of the financing effort and operations were heavily compartmentalized by KSA and Pakistan, so even if CIA money ever made it to bin Laden, they'd have very little (if any) chance of knowing it. And even if the US did know it, would anyone in the US government even know or care much about this oddball young Saudi trustfunder-turned war fundraiser who dabbled in some actual fighting but was frankly, something of a bit player at the time?
They (the US government, including the CIA) really didn't know who he was at the time, let alone, what he was doing and what the significance of it would become.
), MI6, The Mossad and *insert Goverment of country were a terrorist attack has just happened* created ISIS...