Houston founder shares how he's using tech to make digital media more effective and equitable

houston innovators podcast episode 173

This month, Mark Walker is celebrating his company's one year anniversary of going public — only the ninth Black-founded business to accomplish this feat on a U.S. stock exchange. Photo courtesy

After working in both sides of the advertising world, Mark Walker thought he could reimagine a platform that would be more efficient and equitable.

Walker co-founded his company, Direct Digital Holdings, an adtech platform, after serving in several roles — from an early hire at Houston digital media startup Questia to business development director at NRG Energy and COO of EBONY Media. He shares on the Houston Innovators Platform how he took this experience in tech, advertising, and media to create his company's platform.

"NRG Energy gave me a top-down view of the value chain, and Ebony gave me a bottoms-up view of the value chain of how media is purchased," Walker says on the show. "At Direct Digital Holdings, we help companies buy and sell media — and we leverage technology to do it. It's really the culmination of both of those experiences."

With over 30,000 publishers on its platform, Direct Digital makes it easier for its core customers — middle market companies looking to buy into the digital media ecosystem — to tap into these opportunities without the tech know-how they might otherwise need. Walker explains that at EBONY, he saw how small to midsize publications — especially the multicultural ones — were being left out on the ad selling side of the equation. The Direct Digital platform bridges the gap on each end.

Founded in 2018 in partnership with Keith Smith, who went through similar professional experiences, Direct Digital went public exactly one year ago after growing the company through strategic M&A activity. Walker says the decision to IPO made the most sense for his company — though it wasn't an easy process. Direct Digital is only the ninth company founded by a Black entrepreneur to go public on a US stock exchange.

"If you think the process is hard — it actually is," Walker says on the journey to IPO. "We were a privately held company, and we knew we had a good growth trajectory and we looked a couple different options. We decided to go public in a very traditional way."

Walker explains there were some risks involved, but the co-founders ultimately decided to shy away from adding in investors who might not have the same ideas for the company's future.

Direct Digital has been a Houston company from the star — despite the city not being home to a booming adtech ecosystem. Instead, Houston — with its collection of Fortune 500 companies and rich diversity — has allowed the business to stand out.

"If you look at and reflect on how our company has been built — from our board of directors to our leadership and management team — we're a majority minority organization all the way across the board," Walker says. "Diversity is very important to us. It's the lifeblood of our business — especially because we're serving publishers in those communities in big way. And moreso, we think you get the best product, thoughts, and ideas from a diverse workforce, and Houston fits right into that mold for us."

Walker shares more about his company's future, advice on IPO, and what all he's watching in adtech — from AI to streaming — on the podcast. Listen to the interview below — or wherever you stream your podcasts — and subscribe for weekly episodes.


Ad Placement 300x100
Ad Placement 300x600

CultureMap Emails are Awesome

Property Showcase

Axiom Space officially redomiciles its headquarters in Texas

space city

Axiom Space has claimed Houston as its operational home since 2016. And now it can call Texas its official legal headquarters, too.

The spacetech company, which is developing the first commercial space station, Axiom Station, has officially redomiciled its legal headquarters from Delaware to Texas, Axiom announced this week.

Axiom employs approximately 700 people, the majority of whom are in Texas, according to a news release. Its Assembly Integration and Test Facility was built as an anchor of the Houston Spaceport, and the company is also developing next-generation spacesuits at its Houston-based spacesuit lab.

“Texas has demonstrated, consistently and deliberately, that it wants innovative companies to thrive here and has built the policy and regulatory framework accordingly,” Jonathan Cirtain, CEO and president of Axiom Space, said in the release. “For Axiom Space, establishing Texas as both our operational and legal home puts us squarely in a state that understands our mission, supports our industry, and shares in what we are working to achieve.”

Axiom touts Texas's "financial and infrastructural commitments" to the space economy as reasons for the move, including programs and grants from organizations such as the Texas Space Exploration & Aeronautics Research Fund (SEARF), the Texas Space Commission, and the Texas A&M Space Institute.

Axiom was previously awarded a $5.5 million SEARF grant for the development of its orbital data center capabilities last year.

The news comes as energy giant ExxonMobil also announced concrete plans to redomicile its legal headquarters in Texas. Exxon's board of directors unanimously recommended redomiciling in the Lone Star State in March. The company announced this week that the move would become official July 1. The company's operational headquarters is based in Spring, Texas, a Houston-area suburb.

Houston cleantech, space startups named to World Economic Forum cohort

top honor

Two Houston-based startups have been selected to join the World Economic Forum's Technology Pioneers community.

The two-year program aims to help mission-driven, early-stage start-ups scale their innovations through multi-stakeholder initiatives, co-creating partnerships and other gatherings for community members. One-hundred startups are selected each year from around the globe, this year hailing from 23 countries and working in AI, energy, space, biotech markets and more.

Cleantech startup Vaulted Deep was one of 11 energy and climate companies to be named to the cohort. Julia Reichelstein and Omar Abou-Sayed founded the company in 2023. Its technology injects excess organic waste underground to remove carbon dioxide from the atmosphere.

Last year, Vaulted Deep inked a 12-year deal with Microsoft to remove up to 4.9 million metric tons of carbon dioxide from the environment.

The startup has earned several accolades in recent years, including a No. 3 spot on Fast Company’s list of the World’s Most Innovative Companies of 2026. It was also recently named to market intelligence and advisory firm Cleantech Group's annual Global Cleantech 100 list for a second year in a row.

"Waste management is one of the world's great invisible infrastructure systems ... The need for new infrastructure is growing as disposal challenges become more complex and regulations evolve. Vaulted is building the first new disposal pathway for organic waste in decades by putting it deep underground, permanently," the company shared in a LinkedIn post. "This year, we're joining the World Economic Forum's 2026 Tech Pioneers alongside innovators working on the many interconnected challenges shaping our future."

Houston-based Venus Aerospace was also selected to join the cohort, along with six other spacetech companies. The company was founded in 2020 by Sassie and Andrew Duggleby.

The startup specializes in next-generation rocket engine propulsion as a cleaner alternative to traditional combustion engines. The company's rotating detonation rocket engine (RDRE) burns fuel more efficiently and completed a successful high-thrust test flight last year. Venus says it’s the only company in the world that makes a flight-proven, high-thrust RDRE with a “clear path to scaled production.”

"Frontier technologies matter most when they expand what people, industries, and nations can do," Sassie Duggleby, co-founder and CEO of Venus, said in a news release. "For Venus, RDRE does not just represent a more efficient engine. It is a foundation for faster movement, more capable space systems, and new forms of connectivity across the planet. Being named a Technology Pioneer validates the potential of this technology to help shape a future where distance is less limiting."

---

This article originally appeared on our sister site, EnergyCapitalHTX.com.

Houston Methodist receives record $110M gift, names future tower

historic gift

Houston Methodist has received the largest gift in the health system's history to establish new funds for neurological, neuroscience, and women’s health research and treatment.

The $110 million gift comes from Houston-based The Brockman Medical Research Foundation, which supports education and research in the science, medicine and healthcare fields. In response, Houston Methodist announced that it will name its forthcoming 26-story hospital facility the Brockman Centennial Tower.

The tower’s entrance will be named the Anna Margaret Bellows Centennial Hall to honor Anna Margaret Bellows, a young camper who died during the Camp Mystic flooding last summer.

“This extraordinary gift accelerates discovery and transforms how care is delivered,” Dr. Marc Boom, president and CEO of Houston Methodist, said in a news release. “We are grateful to The Brockman Medical Research Foundation for its incredible generosity and vision that will help change the lives of generations of patients. Naming Centennial Tower in recognition of this gift reflects the scale of this commitment and its impact on the future of neuroscience, neurological care and women’s health.”

The gift will be divided into two parts:

  • $100 million will go toward creating an innovation fund within the Houston Methodist Academic Institute and the Houston Methodist Neurological Institute
  • $10 million will be devoted to Houston Methodist's Department of Obstetrics and Gynecology

“This tremendous gift will accelerate translational research that broadens our understanding of neurological and other diseases,” Dr. Jenny Chang, president and CEO of the Houston Methodist Academic Institute, added in the release. “It will allow us to leverage state-of-the-art platforms to detect, diagnose and deliver therapeutics, keeping patient care at the center of our mission.”

The Brockman Centennial Tower is expected to open next year in the Texas Medical Center. Spanning more than 1 million square feet, it will house 400 patient beds, an expanded emergency department, new operating rooms and a rooftop garden. It will be connected to Houston Methodist's flagship Paula and Joseph C. “Rusty” Walter III Tower, which opened in 2018. The Centennial Tower was estimated to cost $1.4 billion when announced in 2022.

In addition to the news of the Brockman gift, Houston Methodist also announced this month that it has launched the Houston Methodist Center for Cell and Gene Therapy and tapped an internationally recognized scientist as its leader.

The new center is focused on discovering and developing innovative and cost-effective therapies for a variety of congenital and acquired diseases, including cancer, HIV and cardiovascular disease.

Dr. Malcolm Brenner has been named as the center's inaugural leader and will assume the role starting in October. He will work alongside scientists and support staff from Baylor College of Medicine and Texas Children's Hospital.

Brenner is a professor of pediatrics, medicine, molecular and human genetics and translational biology at Baylor College of Medicine. He is known for making early advances in using bone marrow transplantation as a form of cell therapy and in engineered immune-cell treatments for cancer and infections, according to a release from Houston Methodist.

“Malcolm Brenner is a pioneer in the field of cell and gene therapy and is uniquely qualified to lead Houston Methodist’s research efforts in this field,” Chang added. “His vision and leadership will play a pivotal role in advancing our work in this space.”

View All Listings