That is a very old crack, as evidenced by the extensive callus development on the perimeter. Such cracks can develop on the trunks of some plants, especially thin-barked plants such as maples, in the winter as so-called "southwest injury" where the bark on the southwest side of the tree alternately heats up in the day and then freezes on very cold, clear winter nights. A longitudinal, vertical crack then develops on the affected tissue. Although the damage is aesthetically problematic, the tree is almost always able to recover and grow well. If this is on the southwest side of the tree (I can't tell) I would suspect this as the cause and that it occurred several years ago. I do not see images of the tree itself, but the vigor of the current-season growth and overall appearance of the tree would help in determining if there is a problem. Feel free to respond with confirmation or if not we can discuss other potential causes. The bottom line, though, is that just based on the submitted photos, as dramatic as it looks, the tree appears to have healed.

Your answer makes perfect sense. Thanks!