Here is conclusive proof that it is impossible to make a boring documentary about Muhammad Ali. Mind you, the folk behind this lacklustre hagiography have certainly tried their hardest to offer an exception to the rule.

The picture’s reason to exist is also the anchor dragging it to mundane depths. Newly available recordings of conversations between Ali and his children fill up large chunks of the documentary with pointless (if cute) jabbering about schoolwork and future ambitions. If this is the stuff they decided to keep, one dreads to think what they threw away.

A scruffy structure that uses inter-titles to introduce discrete episodes – the “manager’s story”, the “brother’s story”, and so on – is rapidly discarded for a conventional juxtaposition of talking heads and archive footage. Some of that is over- familiar: how often do need to learn about the rope-a-dope in the Rumble in the Jungle? Elsewhere, moving images are conspicuous by their absence: there is no footage of Ali in the ring with Joe Frazier.

It doesn't help that the mighty shadow of When We Were Kings hangs so heavily over the enterprise. Whereas that film had the likes of George Plimpton and Norman Mailer offering sage commentary, I Am Ali settles for Tom Jones spouting the sort of anecdote Graham Norton might roll his eyes at. The most jarring letdown in the current film, however, is its extraordinarily drab music. Some drippy folk there. A bit of dull MOR there. Get with it, people. It's not as if the 1960s and 1970s were short of invigorating African- American sounds.

For all that, Ali's allure is so enduring that the film proves hard to entirely resist. What did Plimpton say at the end of When We Were Kings? "What a fighter! What a man!"