It is custom to give characters backstories, and interesting characters generally require them. However, it isn't always easy to supply a believable, non-cliche backstory. It wasn't until Taro that official ultras would receive them, and so we can say a backstory is not needed. It does, however, add significant depth to a tale.
There are several kinds of backstories. It is certainly an option to have a character live a perfectly normal life before the story began: Zach, Moedari, Mater Mundaram and The Hidden One each make use of that trope. Something happens, and they find themselves pushed out of their comfort zone? How do (did) they react?
Another common on is the troubled past. Orion and Lunaram are both examples of this. Something tragic happened in their past, hardening them up and making them less friendly. This is connected to the "Hardened Warrior" past: someone who is used to such things happening but remains friendly, at least on the outside. Ultraman Lugeno is a good example.
So what is a troubled past? Homeworlds wiped out, friends/family/lovers killed, early trauma, or a mix of all of that are common examples. One can add as many twists as he likes, so long as it isn't too confusing. There are interesting variants, but while these are used often, they are still believable.
And then there's the choice between good and evil. Does the past make the character good, or bad? Zoe, for instance, experienced the destruction of her homeworld but became dark, Orion remained with the light. Argentium experienced a tragic war, and Hekar chose evil while Lunaram chose goodness.
Do not forget what happened to Orion afterwards, the Machine War. Remember how Lugeno traveled through time and space sealing universes under Mater Mundaram. Experiences like this help develop the character even further, and give readers reasons to sympathize with them.
Regular life is a struggle as well. Much of Mundaram's backstory is unwritten, but we can be sure it was very similar to some of out own experiences.Creating good backstory is not easy. To be somewhat original as well is even more difficult. It does pay off in the end, but if you feel your backstory isn't good enough, you can always change or remove it.