Most co-founder relationships are built on mutual enthusiasm for an idea, a complementary skill set, and the hope that both people will show up the same way under pressure. That hope gets tested eventually. How much of the partnership survives the test depends almost entirely on what was actually there before the pressure arrived.
Sal Rehmetullah and his sister Suneera built Stacks, an omni-channel payments company for small businesses, from a founding idea in 2014 to over $160 million in recurring revenue, more than $200 million raised, and an exit worth over a billion dollars. Sal is now building Worth AI, a financial intelligence platform designed to give small businesses the kind of credit and lending visibility that has historically only been available to large enterprises.
The question people ask him most often about Stacks isn't about the product or the fundraising. It's about how he and his sister worked together for over a decade without it falling apart. His answer starts with ten schools in twelve years.
Most co-founder relationships are built on mutual enthusiasm for an idea, a complementary skill set, and the hope that both people will show up the same way under pressure. That hope gets tested eventually. How much of the partnership survives the test depends almost entirely on what was actually there before the pressure arrived.
Sal Rehmetullah and his sister Suneera built Stacks, an omni-channel payments company for small businesses, from a founding idea in 2014 to over $160 million in recurring revenue, more than $200 million raised, and an exit worth over a billion dollars. Sal is now building Worth AI, a financial intelligence platform designed to give small businesses the kind of credit and lending visibility that has historically only been available to large enterprises.
The question people ask him most often about Stacks isn't about the product or the fundraising. It's about how he and his sister worked together for over a decade without it falling apart. His answer starts with ten schools in twelve years.
Sal's parents immigrated to the United States and built businesses the way a lot of immigrant entrepreneurs do: out of necessity rather than ambition. There were no college degrees, no corporate job offers, no safety net of the kind that cushions a career change. They owned laundromats and convenience stores and moved the family wherever the work required. By the time Sal and Suneera finished high school, they had attended ten different schools in twelve years.
That kind of upbringing either fractures a sibling relationship or forges it into something most partnerships never develop. For Sal, it did the latter. When you change schools every year, your sibling become your most reliable social constant. You learn to build friendships quickly because you must, but the one relationship that persists through every move is the one you were born into. By the time Sal and Suneera were adults, they had been through enough together that the usual sources of co-founder conflict, misaligned expectations, untested loyalty, different standards under pressure, had already been worked out.
Sal describes the structural advantage plainly. With a spouse, you can have your disagreements, and there are options if those disagreements become permanent. With a sibling, there are no options. You are going to end up at dinner regardless of what was said earlier. That constraint, which sounds like a limitation, turns out to be one of the most reliable trust-building mechanisms available. You stop holding back the hard thing because you know the relationship survives it.
Stacks launched in 2014 with a straightforward observation: small businesses couldn't do what large retailers took for granted. Buying online and returning in store, tap-to-pay, mobile purchasing — those capabilities existed for Macy's. They didn't exist for the small business owner who had grown up watching their immigrant parents build something without those tools. Stacks set out to connect all of it at a price small businesses could actually afford, through a subscription model at a time when everyone else was charging per transaction.
Over the following decade, Stacks onboarded more than a hundred thousand small businesses, processed $40 billion in payment volume, and became one of the top ten largest payment processors in the US. They raised capital in successive rounds as the business grew, recapitalized twice, and eventually exited for over a billion dollars. Sal describes the first recap as a release of pressure after years of sustained effort. The second, at the billion-dollar threshold, produced the same feeling briefly before the next goalpost appeared.
The exit itself was a recognition that the company had entered a stage that needed different leadership. Private equity ownership shifts the operating priorities: EBITDA disciplines tighten, the founder's instinct to protect culture at the expense of margin gets scrutinized, and the skills that built a company from zero to a hundred million in revenue are not always the same skills needed to take it further under institutional ownership. Sal and Suneera were the right people to build Stacks. They were honest enough with themselves to recognize when it was time to bring in people better suited for the next phase.
Suneera used the transition to do what she'd put off for years: be present for her family without a calendar that owned every hour. For Sal, it went differently. He had introduced himself as the co-founder of Stacks for over a decade. Without that identity, the structure of his days disappeared. He worked out, played pickleball, traveled, turned down CEO offers at other companies. Three to six months passed before he and Suneera landed on Worth AI.
Worth AI addresses a problem Sal watched his parents navigate their entire working lives. Small businesses can't access credit on terms that reflect their actual financial health because the tools used to evaluate them were built for a different era, one that required years of W-2 income history, traditional balance sheets, and business plans formatted for bankers who had never met a laundromat owner whose business was thriving but whose paperwork didn't fit the model. Worth AI is building what Sal describes as the business credit score, which is a transparent, data-driven measure of business financial health that financial institutions can use to make better lending decisions and that business owners can use to understand and improve their own position.
The company spent $20 million building direct integrations with the IRS, all 50 secretaries of state, the postal service, and financial data sources across more than 140 countries before it had a commercial product. That's the kind of infrastructure investment that requires conviction in the problem, patience with the timeline, and a co-founder you trust to still be there when the money runs out before the revenue starts.
Sal's account of the Stacks partnership points to something most co-founder conversations skip. The question isn't whether two people get along. People who don't get along don't start companies together. The question is whether the relationship holds when the company is burning cash, a key hire quits, a fundraising round stalls, or the two founders have genuinely different reads on what to do next. Sal and Suneera had been answering that question since they were children. Most co-founders are answering it for the first time at the worst possible moment.
The legal dimension of co-founder relationships sits directly underneath this. A co-founder agreement, an equity split, and vesting schedules are the structural expression of trust, or the absence of it. When the underlying relationship is strong, those documents confirm what both parties already believe. When it isn't, they become the battlefield. Intellectual Strategies and FraxLaw work with founding teams specifically on these structures, because the time to negotiate them is before the company has value, not after.
The exit structure adds another layer. Stacks recapitalized twice before the final exit. Each recapitalization involved a new set of investor rights, a revised understanding of founder roles, and decisions about how much control to retain versus how much capital to accept. Companies that have built strong internal governance before those conversations are in a fundamentally different position than companies that are figuring out their governance structure in the middle of a term sheet negotiation. Sal's description of recognizing when private equity ownership required a leadership transition, and making that call cleanly rather than holding on, reflects a maturity about exit dynamics that most founders develop only after getting it wrong once.
Sal's story about Stacks is sometimes read as a story about family. It's more useful read as a story about what trust actually requires at the co-founder level and how rare it is to have it genuinely in place. Ten schools in twelve years is not a replicable co-founder strategy. The underlying lesson is: the relationship has to be able to survive a direct conversation about the hardest thing, and most co-founder pairs discover too late that theirs can't.
For growing companies, the legal structures around co-founder relationships, equity agreements, vesting, decision-making authority, and exit terms, are the mechanisms that either support a strong partnership or expose a weak one. Getting those structures right early is one of the most consequential things a founding team can do. FraxLaw works with founders at that stage specifically, because the cost of getting it wrong compounds with every year the company grows.
For more on what companies consistently get wrong before they're ready to exit, read PATTERN INSIGHT 3 — The Exit Trap.
Listen to Sal Rehmetullah's episode here.
