Demeco Ryans (/dɪˈmiːkoʊ/ dih-MEE-koh; born July 28, 1984) is an American professional football coach and former linebacker who is the head coach for the Houston Texans of the National Football League (NFL). He played college football for the Alabama Crimson Tide, where he was a unanimous All-American. Ryans was selected by the Texans in the second round of the 2006 NFL draft, where he was recognized as the Defensive Rookie of the Year. Ryans was selected to two Pro Bowls before being traded to the Philadelphia Eagles in 2012, where he spent four seasons before retiring.

Ryans joined the San Francisco 49ers as a coaching assistant in 2017 and coached the inside linebackers from 2018 to 2020 before being named their defensive coordinator in 2021. The following season, he was named NFL Assistant Coach of the Year after the 49ers finished with the top-ranked defense, leading in scoring and total yards allowed. Ryans was hired as the head coach for the Texans in 2023 and took them to the playoffs in his first season in that role.

Ryans was born on July 28, 1984, in Bessemer, Alabama. He attended Jess Lanier High School in Bessemer, where he played high school football. As a senior, Ryans had 135 tackles, 11 sacks, two forced fumbles, and two interceptions. Considered a three-star recruit by Rivals.com, he was listed as the No. 39 inside linebacker prospect in the nation from the class of 2002. Ryans picked Alabama over Mississippi State.

Ryans attended the University of Alabama, where he played outside linebacker for coach Mike Shula's Alabama Crimson Tide football team from 2002 to 2005.

Ryans started his career by earning a role on special teams and backup linebacker in his first season. By making great improvements every year in his college career, Ryans went on to become the SEC's Defensive Player of the Year for his performance in 2005. Later on, he attributed much of his collegiate success to his defensive coordinator at Alabama, Joe Kines. Ryans was named the 2006 Cotton Bowl Classic defensive MVP in their 13–10 victory over Texas Tech. Following his senior season, Ryans earned the Lott Trophy for his combination of athletic excellence and off-the-field achievements and was recognized as a unanimous All-American.

Ryans was selected with the first pick of the second round (33rd overall) in the 2006 NFL draft by the Texans. He was the highest-selected Alabama linebacker since Dwayne Rudd was selected 20th overall by the Minnesota Vikings in 1997. Though Ryans had been an outside linebacker in college, he earned the starting middle linebacker position due to his excellent performance in the preseason. In his first game, Ryans recorded a league-high 12 solo tackles against the Philadelphia Eagles. He had an overwhelming impact as a rookie, leading the Texans in tackles in the first half of the 2006 season. Ryans was named AFC Defensive Player of the Week for his performance during a Week 13 23–14 victory over the Oakland Raiders in which he recorded 15 tackles, three pass deflections, a sack, a forced fumble, a fumble recovery, and an interception.

Ryans was named the AP NFL Defensive Rookie of the Year after finishing second in the league with 155 total tackles (Zach Thomas led the NFL with 165), 31 more tackles than the next rookie (Detroit Lions linebacker Ernie Sims). Ryans was also named to the NFL All-Rookie Team. In 2007, Ryans was named a second-team All-Pro linebacker and was selected to the Pro Bowl in 2007 and 2009.

On March 30, 2010, Ryans signed a six-year extension worth $48 million, including $21.75 million guaranteed.