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.


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10 promising Houston startups that made headlines in 2025

year in review

Editor's note: As we reflect on 2025, we're looking back at the stories and startups that made waves in Houston's innovation scene. These 10 startups reached memorable milestones, won prestigious awards, found creative solutions, and disrupted their industries.

Persona AI: Houston humanoid robotics startup inks new deal to deploy its rugged robots

A concept design rendering of Persona AI's humanoid robot. The company is expanding at the Ion and plans to deliver prototype humanoids by the end of 2026 for complex shipyard welding tasks. Rendering courtesy Persona AI.

Persona AI is building modularized humanoid robots that aim to deliver continuous, round-the-clock productivity and skilled labor for "dull, dirty, dangerous, and declining" jobs. The company was founded by Houston entrepreneur Nicolaus Radford, who serves as CEO, along with CTO Jerry Pratt and COO Jide Akinyode. It raised $42 million in pre-seed funding this year and is developing its prototype of a robot-welder for Hyundai's shipbuilding division, which it plans to unveil in 2026. The company won in the Deep Tech Business category at this year's Houston Innovation Awards. Continue reading.

Rheom Materials: Houston startup unveils its innovative leather alternative at the rodeo

Rheom Materials presented its bio-based alternative, Shorai, a 93 percent bio-based leather, at the rodeo and plans to scale it up this year. Photos courtesy Rheom Materials

Rheom Materials presented its scalable, bio-based alternative known as Shorai, a 93 percent bio-based leather, through two custom, western-inspired outfits that showed off cowboy flair through a sustainable lens at the Houston Livestock Show and Rodeo earlier this year.

Next up, the company said it aimed to scale production of Shorai, the Japanese word for “future,” at a competitive price point, while also reducing its carbon footprint by 80 percent when compared to synthetic leather. The company also made a large-scale production partnership with a thermoplastic extrusion and lamination company, Bixby International, this year. Continue reading.

Koda Health: Houston digital health platform Koda closes $7 million funding round

Tatiana Fofanova and Dr. Desh Mohan, founders of Koda Health, which recently closed a $7 million series A. Photo courtesy Koda Health.

Houston-based digital advance care planning company Koda Health closed an oversubscribed $7 million series A funding round this year. The round, led by Evidenced, with participation from Mudita Venture Partners, Techstars and Texas Medical Center, will allow the company to scale operations and expand engineering, clinical strategy and customer success. Koda Health, saw major growth this year by integrating its end-of-life care planning platform with Dallas-based Guidehealth in April and with Epic Systems in July. The company won the Health Tech Business category at the 2025 Houston Innovation Awards. Continue reading.

Veloci Running: Student-led startup runs away with prestigious prize at Rice competition

The H. Albert Napier Rice Launch Challenge awarded $100,000 in equity-free funding to student-led startups, including first-place finisher Veloci Running. Photo courtesy of Rice University.

Veloci Running took home the first-place prize and $50,000 at the annual Liu Idea Lab for Innovation and Entrepreneurship's H. Albert Napier Rice Launch Challenge. The company was founded by Tyler Strothman, a former track and field athlete and senior at Rice, majoring in sport management. Inspired by the foot pain he suffered due to the narrow toe boxes in his running shoes, Strothman decided to create a naturally shaped shoe designed to relieve lower leg tightness and absorb impact. Additional prize winners included SteerBio, Kinnections, Labshare and several others. Continue reading.

Square Robot Inc.: Houston robotics co. unveils new robot that can handle extreme temperatures

The new robot eliminates the need for humans to enter dangerous and toxic environments. Photo courtesy of Square Robot

Houston- and Boston-based Square Robot Inc.'s newest tank inspection robot became commercially available and certified to operate at extreme temperatures this fall. The new robot, known as the SR-3HT, can operate from 14°F to 131°F, representing a broader temperature range than previous models in the company's portfolio. According to the company, its previous temperature range reached 32°F to 104°F. The company also announced a partnership with downstream and midstream energy giant Marathon Petroleum Corp. (NYSE: MPC) last month. Continue reading.

Bot Auto: Houston autonomous trucking co. completes first test run without human intervention

Bot Auto completed its first test run without human assistance in Houston. Photo courtesy Bot Auto.

Houston-based Bot Auto, an autonomous trucking company, completed its first test run without human assistance earlier this year. Bot Auto conducted the test in Houston. The transportation-as-a-service startup added that this milestone “serves as a validation benchmark, demonstrating the maturity and safety of Bot Auto’s autonomy stack and test protocols.” This summer, founder Xiaodi Hou told the Front Lines podcast that Bot Auto had raised more than $45 million. Continue reading.

Nomad: Screen-free hiking app developed in Houston earns 'Best of the Best' award

NOMAD aims to help hikers stay in the moment while still utilizing technology. Photo courtesy UH.

An AI-powered, screen-free hiking system developed by Varshini Chouthri, a recent industrial design graduate from the University of Houston, received this year's Red Dot’s “Best of the Best” award, which recognizes the top innovative designs around the world. Known as NOMAD, the system aims to help users stay in the moment while still utilizing technology. Continue reading.

Little Place Labs, Helix Earth, Tempest Droneworx: Houston startups win big at SXSW 2025 pitch competition

Two Houston startups won the SXSW Pitch showcase in their respective categories. Photo via Getty Images

Houston had a strong showing at the SXSW Pitch showcase in Austin this year, with several local startups claiming top prizes in their respective categories.

Little Place Labs, a Houston space data startup, won the Security, GovTech & Space competition. Clean-tech company Helix Earth, which spun out of Rice University and was incubated at Greentown Labs, won in the Smart Cities, Transportation & Sustainability contest. Tempest Droneworx, a Houston-based company that provides real-time intelligence collected through drones, robots and sensors, won the Best Speed Pitch award. Continue reading.

6 Houstonians named to prestigious national group of inventors

top honor

Six Houston scientists and innovation leaders have been named to the National Academy of Inventors’ newest class of fellows. The award is the highest professional distinction awarded to academic inventors by the NAI.

The 2025 class is made up of 169 fellows who hold more than 5,300 U.S. patents, according to the organization. The group hails from 127 institutions across 40 U.S. states.

The Houston-based inventors are leading fields from AI to chemistry to cancer research.

“NAI Fellows are a driving force within the innovation ecosystem, and their contributions across scientific disciplines are shaping the future of our world,” Paul R. Sanberg, president of the National Academy of Inventors, said in a news release. “We are thrilled to welcome this year’s class of Fellows to the Academy. They are truly an impressive cohort, and we look forward to honoring them at our 15th Annual Conference in Los Angeles next year.”

The 2025 list of Houston-based fellows includes:

  • Vineet Gupta, Vice President for Innovation, Technology Development and Transfer at the University of Texas Medical Branch
  • Eva Harth, chemistry professor at the University of Houston
  • Dr. Raghu Kalluri, Professor and Chairman of the Department of Cancer Biology at The University of Texas MD Anderson Cancer Center
  • Sanjoy Paul, Executive Director of Rice Nexus and AI Houston and Associate Vice President for Technology Development at Rice University
  • Dr. Jochen Reiser, President of the University of Texas Medical Branch and CEO of UTMB Health System
  • Todd Rosengart, Professor and Chair of the Department of Surgery at Baylor College of Medicine

"It is a great honor to be named a Fellow of the NAI. It is deeply gratifying to know that the work my students and I do — the daily push, often in small steps — is seen and recognized," Harth added in a news release from UH.

The 2025 fellows will be honored and presented with their medals by a senior official of the United States Patent and Trademark Office at the NAI Annual Conference this summer in Los Angeles.