Author's Note: Background for my next several character builds ...
In 1992, a mysterious figure who called himself the Seer recruited a team of superhumans whose powers (and some cases activities) had made them into outcasts. The Seer's purpose was to prevent certain events, which he dubbed "temporal trigger points", from going "the wrong way". The Seer was in fact Dr. Jeremiah Prophet, psychologist, profiler and distant cousin to the more famous Prophet family, who kept his connection with Colonel Jackson Cross of the United States Army a deep secret even from his teammates.
Over the next few years, the Vanguard did quite a bit of good, but generally kept a very low profile in comparison to the Freedom League or the Justice Foundation. That came to an end in 2001, after they foiled an attempt by the Hypersapiens to engage in large-scale mind control, using UNIQUE (the United Nations International Quorum of Unaligned Exceptionals) as pawns. While successfully resolved, the situation was a serious embarrassment for UNISON, and for the United Nations in general, and prompted the dissolution of UNIQUE.
Soon afterwards, Colonel Cross (by now retired from the Army) joined UNISON and began laying the groundwork for a new team of superhuman operatives. He turned to his old ally for help. The team's first major recruit was the mysterious Luminary, in 2002, and the others followed soon after. The team's quick response to the Evanston incident, in 2006, catapulted them into the spotlight, and they've remained there ever since. (The original Vanguard, or at least those who stuck with Prophet after the changeover, are members of the other Mission Teams.)
Generally, relations between the Vanguard and the other teams, such as the Freedom League, are friendly. The team does good work, after all, even though the rest of the heroes are often a bit disconcerted by the sheer amount of arranged media attention that attends every one of the Vanguard's activities. Nonetheless, the consensus is that if that's the way that the Vanguard wants to do things, then let them -- so long as nobody gets hurt in the process. The more suspicious heroes, like the Raven, are keeping a careful watch on UNPAX; regardless of the good intentions of the heroes, in a team beholden to a mundane organization like this one, it's important to keep an eye on the people who are actually in charge.
That group has gone through some changes recently. In 2015, Colonel Cross retired from active duty after a serious heart attack, though he remains an adviser to the agency he helped to found. Jeremiah Prophet was promoted into the Executive Director's chair, with Vanessa Ashe, the first operator of the Valkyrie power armor, given his former office as Deputy Director of Field Operations. Four months later, Jeremiah Prophet disappeared. He'd had a tendency to engage in unexplained and unaccounted absences of this nature during his time as Deputy Director, but had stated that these were at an end upon his promotion to the agency's top seat. Furthermore, none of these absences had lasted as long as this one has, up to the current day.
With some reluctance, Vanessa Ashe accepted the title of Executive Director pro tem until the Prophet situation can be resolved, with the Field Operations desk being given to Niara Cheboi, alias Matron. Under her supervision, the Vanguard has successfully prevented Malador the Mystic from completing a global mind control scheme, among other triumphs, but also suffered a serious loss during an operation in Canada, which resulted in the apparent death of founding member Luminary. Relations with the Freedom League have also suffered following Matron's decision not to send her teams into the Yellowstone Battle, but rather attempt to organize a worst-case scenario response to the situation.
The possibility that Jeremiah Prophet's disappearance might involve the Vision which led him to form Vanguard has been discussed, but Jackson Cross, the only other individual who knows the full details of that episode, has refused to discuss it with anyone.